Project Euler Forum

This will probably lead to a change in the problem description, so I'll let you guys know here,

I've found a mistake with this problem. I've laid my entire strategy out in the problem 44 thread, so check it out there:
https://projecteuler.net/thread=44&page=9#last

Cheers, Lukas

It was a false positive during your code - answered in the internal thread.

Remember to calculate the correct difference!

I was iterating "a difference" and lost track that it is actually part of the answer,
but not the correct part.

So with the example and let's assume 48 is pentagonal, I took:
P4 = P8-P7 = 22 as the solution, using P4 is "the" difference, but it's not!

Correct needs to be:
D = P7-P4 = 48 (again, assumption 48 is pentagonal)