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PROJECT EULER · #0045

Triangular, Pentagonal, and Hexagonal

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Triangle, pentagonal, and hexagonal numbers are generated by the following formulae:

Triangle   Tn=n(n+1)/2   1,3,6,10,15,
Pentagonal   Pn=n(3n1)/2   1,5,12,22,35,
Hexagonal   Hn=n(2n1)   1,6,15,28,45,

It can be verified that T285=P165=H143=40755.

Find the next triangle number that is also pentagonal and hexagonal.

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