def main(verbose=False):
prime_max = 10 ** 5
PRIMES = sieve(prime_max)
found = []
n = 2
while len(found) < 25:
n += 1
if n > prime_max:
prime_max *= 10
PRIMES = sieve(prime_max)
if n % 2 == 0 or n % 5 == 0 or n in PRIMES:
continue
basis = n
if n % 3 == 0:
basis = 9 * n
if (n - 1) % order_mod_n(10, basis) == 0:
found.append(n)
if verbose:
return ('%s.\nAs a check, the first five values are calculated to be '
'%s, as stated.' % (sum(found),
', '.join(str(num) for num in found[:5])))
else:
return sum(found)
def main(verbose=False):
PRIMES = sieve(10 ** 5)
running_sum = 0
for prime in PRIMES:
if not prime_divides_repunit_power10(prime):
running_sum += prime
return running_sum
def main(verbose=False):
prime_factors_hash = {}
MINIMUM_SOLUTIONS = 4*(10**6)
# P^k < 10**7 (10 mil)
powers = [power_up_to_digits(prime, 7)
for prime in [3, 5, 7]]
products = [reduce(operator.mul, triple) for
triple in list(i_product(*powers))]
products = [product for product in sorted(products)
if product > 2*MINIMUM_SOLUTIONS][:20]
PRIMES = sieve(100)
max_prod = 10**21
res = []
for product in products:
factors = prime_factors(product, unique=False, hash_=prime_factors_hash)
factors = [(factor - 1)/2 for factor in factors][::-1]
curr_prod = 1
for i, exp in enumerate(factors):
curr_prod = curr_prod*(PRIMES[i]**exp)
if curr_prod < max_prod:
max_prod = curr_prod
return max_prod
def main(verbose=False):
# layer/primes
# 2/3
# 1581/835
# 3536/1677
# 5000/2249
# 13121/5248, winning layer
# ratio >= .1 iff 10*(primes/total) >= 1 iff 10*primes >= total
# iff 10*primes >= 4*index - 3
FAILURE_POINT = 10 ** 9
PRIMES = sieve(int(sqrt(FAILURE_POINT)) + 1)
layer = 2
num_primes = 3
while 10 * num_primes >= 4 * layer - 3:
layer += 1
candidates = [(2 * layer - 1) ** 2 - 2 * (layer - 1) * i
for i in range(1, 4)]
if candidates[-1] >= FAILURE_POINT:
raise ValueError("Sieve was not big enough, restart function")
for candidate in candidates:
if is_prime(candidate, primes=PRIMES, failure_point=FAILURE_POINT):
num_primes += 1
side_length = 2 * layer - 1 # 2*(layer - 1) + 1
return side_length
def main(verbose=False):
PRIMES = sieve(10 ** 7)
running_sum = 0
for prime in PRIMES:
if prime not in [2, 5]:
running_sum += inverse_mod_n(10, prime)
return running_sum
def main(verbose=False):
primes = sieve(100)
MAX_n = 10 ** 16
product_factor_pairs = [(1, 0)]
product_hash = {0: [1]}
for num_factors in range(1, 13 + 1):
product_hash[num_factors] = []
# (1,0) becomes
# (1,0), (p, 1) becomes
# (1,0), (p, 1), (q,1), (q*p, 2) etc.
for prime in primes:
to_add = []
for product, num_factors in product_factor_pairs:
if prime * product < MAX_n:
to_add.append((prime * product, num_factors + 1))
product_hash[num_factors + 1].append(prime * product)
product_factor_pairs += to_add
result = 0
sign = -1
for num_factors in range(4, 13 + 1):
sign = -sign
PIE_factor = sign * choose(num_factors - 1, 3)
current_sum = 0
for product in product_hash[num_factors]:
current_sum += MAX_n / product # integer division
result += PIE_factor * current_sum
return result
def all_circular(n):
# the number of digits limits the size of all permutations
digs = len(str(n))
possible_primes = [2, 5] + \
[prime for prime in sieve(10**digs - 1)
if contains_only_digits(prime, [1, 3, 7, 9])]
return [prime for prime in possible_primes if prime <= n
and all_circular_perm_in(prime, possible_primes)]
def main(verbose=False):
# By the prime number theorem, pi(x) =~ x/ln(x)
# pi(x) >= 10001 when x >= 10001 ln(x)
# To be safe, we'll double it and solve
# x = 20002 ln(x)
# We are left with approximately 248490
primes = sieve(248490)
return primes[10001 - 1]
def main(verbose=False):
# sieve(6000) will do it (answer is 5777)
curr = 9
primes = sieve(5777)
while is_possible(curr, primes):
curr += 2
while curr in primes:
curr += 2
return curr
def main(verbose=False):
problem_max = 10 ** 6
count = 0
PRIMES = sieve(problem_max)
max_L = int(round((sqrt(12 * problem_max - 3) - 3) / 6))
for L in xrange(1, max_L + 1):
difference = (L + 1) ** 3 - L ** 3
if difference in PRIMES:
count += 1
return count
def prime_sequence_exists(length, digits, primes=[]):
"""
Returns True if a sequence of length consecutive primes which sums
to less than 10**digits also sums to a prime number
"""
cap = 10**digits
if primes == []:
primes = sieve(cap)
sums = [sum(seq) for seq in all_prime_seqs(length, digits, primes)]
return (set(sums).intersection(primes) != set())
def main(verbose=False):
problem_max = 10 ** 6
PRIMES = sieve(problem_max)
# ignore zero index
ratios = [(1, index) for index in range(problem_max + 1)]
for prime in PRIMES:
ratios[prime::prime] = [((ratio * prime * 1.0) / (prime - 1), index)
for ratio, index in ratios[prime::prime]]
ratios.sort(key=lambda pair: pair[0], reverse=True)
return ratios[0][1]
def matches(problem_max):
PRIMES = sieve(problem_max)
phi_list = range(problem_max + 1) # ignore zero index
for prime in PRIMES:
phi_list[prime::prime] = [(val / prime) * (prime - 1) for val in
phi_list[prime::prime]]
cands = [(val, phi_list[val]) for val in range(2, problem_max + 1)
if same_digits(val, phi_list[val])]
cands.sort(key=lambda cand: (cand[0] * 1.0) / cand[1])
return cands[0][0]
def main(verbose=False):
PRIMES = sieve(10 ** 6)
prime_index = 3 # p0=2, p1=3, and p2=5 are false positives
matches = []
while len(matches) < 40:
prime = PRIMES[prime_index]
if prime_divides_repunit_power10(prime, 9):
matches.append(prime)
prime_index += 1
return sum(matches)
def main(verbose=False):
# Since p_n > 70710, to be safe let's multiply by 10
PRIMES = sieve(707100)
# The odd primes are the even indices here
prime_index = 1
product = 2*(1*2) # p_1 = 2
while product < 10**10:
prime_index += 2
prime = PRIMES[prime_index-1]
product = 2*(prime_index*prime)
return prime_index
def all_radicals(n):
PRIMES = sieve(n)
result = {1: 1}
for i in range(2, n + 1):
if i in PRIMES:
result[i] = i
prime, quotient = first_prime_divisor(i, PRIMES)
if quotient % prime == 0:
result[i] = result[quotient]
else:
result[i] = result[quotient]*prime
return result
def main(verbose=False):
PRIMES = sieve(10 ** 6 + 3) # 10**6 + 3 is the final value of p_2
running_sum = 0
for index in range(2, len(PRIMES) - 1):
p_1 = PRIMES[index]
p_2 = PRIMES[index + 1]
ten_inverse = inverse_mod_n(10, p_2)
digits = len(str(p_1))
k = (ten_inverse ** digits) * (p_2 - p_1) % p_2
running_sum += int('%s%s' % (k, p_1))
return running_sum
def longest_prime_sequence(digits, primes=[]):
"""
Returns the length of the most consecutive primes which sum
to a prime and sum to less then 10**digits
"""
if primes == []:
primes = sieve(10**digits)
max_length = max_prime_length(digits, primes)
for length in range(max_length, 0, -1):
if prime_sequence_exists(length, digits, primes):
return length
raise ValueError("Algorithm failed")
def main(verbose=False):
MAX_n = 10 ** 6 - 1
distinct_solutions = 10
PRIMES = sieve(int(sqrt(MAX_n)) + 1)
factor_hash = {}
count = 0
for n in range(1, MAX_n + 1):
factor_list = factors(n, factor_hash, PRIMES)
if len(num_solutions(factor_list)) == distinct_solutions:
count += 1
return count
def main(verbose=False):
MAX_n = 987654321
PRIMES = sieve(int(sqrt(MAX_n)))
# A 9 digit pandigital will have digit sum 45, so can't be prime
# must be divisible by 9
for i in range(8, 1, -1):
cand = [str(dig) for dig in range(1, i + 1)]
cand = int("".join(cand))
candidates = sorted(all_permutations_digits(cand))[::-1]
for candidate in candidates:
if is_prime(candidate, primes=PRIMES, failure_point=MAX_n):
return candidate
raise ValueError("No prime was found, algorithm busted.")
def main(verbose=False):
D = 10 ** 6
PRIMES = sieve(int(sqrt(D)) + 1)
# We seek |F_D| = 1 + sum_{i in 1 to D} PHI(i)
# 2*sum_{i in 1 to D} PHI(i) = 1 + sum_{i in 1 to D} MU(i) floor(D/i)**2
# 2*|F_D| = 3 + sum_{i in 1 to D} MU(i) floor(D/i)**2
mu_hash = {1: 1}
running_sum = D ** 2 # i = 1
for i in range(2, D + 1):
running_sum += mu(i, mu_hash, PRIMES) * (int(floor(D * 1.0 / i)) ** 2)
# They don't include 0/1 or 1/1 so we subtract 2
return ((3 + running_sum) / 2 - 2)
def find_first_n_truncatable(n, max_n):
result = []
primes = sieve(max_n)[4:] # We don't include 2, 3, 5, or 7
for prime in primes:
if is_truncatable_prime(prime, primes):
result.append(prime)
if len(result) == n:
return result
if len(result) < n:
raise Exception("Not enough found, raise max_n")
return result
def main(verbose=False):
PRIMES = sieve(10 ** 6)
for prime in PRIMES:
digit, count = most_common_digit(prime)
if count > 2:
candidates = find_and_replace(prime, digit)
match_count = 0
for candidate in candidates:
if candidate in PRIMES:
match_count += 1
if match_count == 8:
return prime
def main(verbose=False):
MAX_n = 10 ** 8
# q <= p, q**2 <= pq = n < max_n, q < sqrt(max_n)
# 2 <= q, 2p <= pq < max_n, p < max_n/2
# Given q, pq < max_n, p < max_n/q
PRIMES = sieve(MAX_n / 2) # integer division intended
result = 0
q_max_index = bisect(PRIMES, sqrt(MAX_n))
for q_index in range(q_max_index + 1):
p_min_index = q_index
p_max_index = bisect(PRIMES, MAX_n * 1.0 / PRIMES[q_index])
result += p_max_index - p_min_index
return result
def relevant_triples(n):
result = []
top_sieve = sieve(max_p(2, n))
next3 = [prime for prime in top_sieve
if prime <= max_p(4, n)]
for p3 in next3:
next2 = [prime for prime in top_sieve
if prime <= max_p(3, n - p3 ** 4)]
for p2 in next2:
next1 = [prime for prime in top_sieve
if prime <= max_p(2, n - p3 ** 4 - p2 ** 3)]
for p1 in next1:
if p1 ** 2 + p2 ** 3 + p3 ** 4 < n:
result.append(p1 ** 2 + p2 ** 3 + p3 ** 4)
return set(result)
def main(verbose=False):
primes = [prime for prime in sieve(10000) if prime > 999]
primes_by_digits = {}
for prime in primes:
key = "".join(sorted(digit for digit in str(prime)))
# sets value to [] if not set, returns value at key
primes_by_digits.setdefault(key, []).append(prime)
result = []
for key in primes_by_digits:
candidate = primes_by_digits[key]
if len(candidate) >= 3:
soln = find_arithmetic(candidate)
if soln:
result.append("".join(str(num) for num in sorted(soln)))
return result[0]
def max_prime_length(digits, primes=[]):
"""
Returns the length of the longest string of primes
(starting at 2,3,5,...) that will sum to less 10**digits
"""
cap = 10**digits
if primes == []:
primes = sieve(int(4 * sqrt(cap)))
count = 0
num_primes = 0
for prime in primes:
if count + prime < cap:
count += prime
num_primes += 1
else:
return num_primes
raise ValueError("max_prime_length failed logic.")
def main(verbose=False):
PRIMES = sieve(86238)
b_choices = [prime for prime in PRIMES if prime < 1000]
candidates = [(a, b, polynomial_consecutive_primes(a, b, PRIMES))
for a in range(-999, 999 + 1)
for b in b_choices]
quantities = [entry[2] for entry in candidates]
winner = candidates[quantities.index(max(quantities))]
prod = winner[0]*winner[1]
a = winner[0]
b = winner[1]
max_vals = winner[2]
if verbose:
return ('%s.\nSetting a = %s and b = %s produces '
'%s consecutive primes.' % (prod, a, b, max_vals))
else:
return prod
def main(verbose=False):
MAX_n = 10 ** 4
PRIMES = sieve(MAX_n)
partner_hash = prime_concat_partners(PRIMES, PRIMES, MAX_n ** 2)
valid = possible_pairings(partner_hash, 5)
min_sum = 10 ** 10
min_set = None
for subset in valid:
if sum(subset) < min_sum:
min_sum = sum(subset)
min_set = subset
min_set = [str(prime) for prime in sorted(min_set)]
if verbose:
return '%s.\nThis is obtained with the primes %s.' % (
min_sum, ', '.join(min_set))
else:
return min_sum
def main(verbose=False):
TOTAL = 2000
MAX_n = 10 ** 6
PRIMES = sieve(MAX_n)
# Constant, rather than linear lookup
prime_bools = [False] * (MAX_n + 1)
for prime in PRIMES:
prime_bools[prime] = True
count = 2
current = 2
layer = 3
first_corner = 8 # Value of first corner in layer
last_corner = 19 # Value of last corner in layer
six_shared = 11 # prime candidate shared by both corners,
# with a difference of 6
six_first = 13 # prime candidate for first corner, diff 6
six_last = 17 # prime candidate for last corner, diff 6
twelve_first = 29 # prime candidate for first corner, diff 12
twelve_last = 17 # prime candidate for last corner, diff 12
while count < TOTAL:
if twelve_first > MAX_n:
raise Exception("Primes not large enough")
if prime_bools[six_shared]:
if prime_bools[six_first] and prime_bools[twelve_first]:
current = first_corner
count += 1
if count < TOTAL:
if prime_bools[six_last] and prime_bools[twelve_last]:
current = last_corner
count += 1
six_shared, six_last = six_last, six_last + 6
six_first += 6
twelve_last, twelve_first = twelve_first, twelve_first + 12
first_corner += 6 * (layer - 1)
last_corner += 6 * layer
layer += 1
return current