tritriangular number - Wolfram|Alpha

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Input interpretation

tritriangular number

Definition

A number of the form
Tt_n = ((n + 2
2)
2) = 1/8 n(n + 1)(n + 2)(n + 3)
(Comtet 1974, Stanley 1999), where (n
k) is a binomial coefficient. The first few values are 3, 15, 45, 105, 210, 378, 630, ... (OEIS A050534). The generating function for the tritriangular numbers is
(3x)/(1 - x)^5 = 3x + 15x^2 + 45x^3 + 104x^4 + ....

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Related term

triangular number

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