Pyramid #257
Generating function
$$U_{257}(x, y) = \frac{- \sqrt{1 - 4 x} + \sqrt{2} \sqrt{8 x^{2} y - 2 x - \sqrt{1 - 4 x} + 1} + 1}{4 x}$$
Explicit formula
$$T_{257}(n, m, k) = \begin{cases}1&\text{if m=0 and n = 0} ,\ \\\frac{\left(-1\right)^{m - 1} k {\binom{- k + 2 m - 1}{m - 1}}}{m}&\text{if n=0} ,\ \\\frac{\left(-1\right)^{m + n - 1} k {\binom{- k + 2 m}{m}} {\binom{- k + 2 m - n - 1}{n - 1}}}{n}&\text{if n>0} \end{cases} $$
Data table
1 1 -1 2 -5 14 -42
1 -1 3 -1 35 -126 462
2 -1 0 1 -7 378 -1848
5 -2 1 0 35 -42 3234
14 -5 3 0 0 126 -231
42 -14 9 -2 0 0 462
132 -42 28 -1 0 0 0
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