def f(n):
"""10s of microseconds to compute for 20"""
prod = 1
prime_divs = primes_less(n)
for a in range(2, n + 1):
if prod % a == 0:
continue
else:
prod *= least_prime_div(a, prime_divs)
return prod
def f(n):
"""Several seconds :("""
return sum(primes_less(n))
def find_pairs(N):
ps = primes_less(N+1)
return [(a, b) for b in ps for a in range(-b, N+1)]