def addPrime():
p = next(piter)
pstr = str(p)
conc = set()
for q in concatable.iterkeys():
qstr = str(q)
if isPrime(int(pstr + qstr)) and isPrime(int(qstr + pstr)):
conc.add(q)
concatable[p] = conc
return (p, conc)
def solve():
leftTruncate = set([2,3,5,7])
rightTruncate = set([2,3,5,7])
bothTruncate = set()
magnitude = 1
while len(bothTruncate) < 11:
magnitude *= 10
lt2 = set()
for p in leftTruncate:
for d in xrange(1,10):
x = d * magnitude + p
if isPrime(x):
lt2.add(x)
leftTruncate = lt2
rt2 = set()
for p in rightTruncate:
for d in (1,3,7,9):
x = p * 10 + d
if isPrime(x):
rt2.add(x)
rightTruncate = rt2
bothTruncate.update(leftTruncate & rightTruncate)
return sum(bothTruncate)
