Pyramid #1256
Pyramid #1257
Pyramid #1258
Generating function
$$U_{1257}(x, y) = \frac{1}{\left(1 - y\right) \left(- \frac{x}{1 - y} + 1\right)^{3}}$$
Explicit formula
$$T_{1257}(n, m, k) = {\binom{3 k + n - 1}{n}} {\binom{k + m + n - 1}{m}}$$
Data table
1 1 1 1 1 1 1
3 6 9 12 15 18 21
6 18 36 6 9 126 168
1 4 1 2 35 56 84
15 75 225 525 105 189 315
21 126 441 1176 2646 5292 9702
28 196 784 2352 588 12936 25872
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