Pyramid #1255
Pyramid #1256
Pyramid #1257
Generating function
$$U_{1256}(x, y) = \frac{\left(y + 1\right)^{3}}{\left(- x \left(y + 1\right)^{3} + 1\right)^{3}}$$
Explicit formula
$$T_{1256}(n, m, k) = {\binom{3 k + 3 n}{m}} {\binom{3 k + n - 1}{n}}$$
Data table
1 3 3 1 0 0 0
3 18 45 6 45 18 3
6 54 216 504 756 756 504
1 12 66 22 495 792 924
15 225 1575 6825 20475 45045 75075
21 378 3213 17136 6426 179928 389844
28 588 588 3724 16758 569772 1519392
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