euler.py

class Pentagonals(object):
    def __init__(self):
        self._nums={}

    def add_pent(self):
        n=len(self._nums)+1
        self._nums[n-1]=(n*((3*n)-1)/2)

    def is_pent(self, n):
        return n in self._nums

    def __getitem__(self, n): #special function accessible via []
        while n>=len(self._nums):
            self.add_pent()
        return self._nums[n-1]

a = 2
finished=False
pents=Pentagonals()

while not finished:
    for b in range(1, a):
        a_pent, b_pent = pents[a], pents[b]
        if pents.is_pent(a_pent-b_pent) and pents.is_pent(a_pent+b_pent):
            print
            print a_pent-b_pent
            finished=True
    a+=1
    print str(a) + "\r",