Triangular square number
From Wikipedia, the free encyclopedia.

A triangular square number is a number which is both a triangular number and a perfect square. There is an infinity of triangular squares, given by the formula

The k^th triangular square N_k is equal to the s^th perfect square and the t^th triangular number, such that

,

t is given by the formula

.

As k becomes larger, the ratio t/s approaches the square root of two:

The original article can be found at: http://en.wikipedia.org/wiki/Triangular_square_number.
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