Pyramid #414
Generating function
$$U_{414}(x, y) = \frac{\sqrt{4 x + \frac{\left(\sqrt{4 y + 1} + 1\right)^{2}}{4}}}{2} + \frac{\sqrt{4 y + 1}}{4} + \frac{1}{4}$$
Explicit formula
$$T_{414}(n, m, k) = \begin{cases}1&\text{if m=0 and n=0} ,\ \\\frac{k {\binom{k - n - 1}{n - 1}}}{n}&\text{if m=0} ,\ \\\frac{\left(-1\right)^{m - 1} k {\binom{k - n - 1}{n}} {\binom{- k + 2 m + 2 n - 1}{m - 1}}}{m}&\text{if m>0} \end{cases} $$
Data table
1 1 -1 2 -5 14 -42
1 -1 2 -5 14 -42 132
-1 3 -9 28 -9 297 -1001
2 -1 4 -15 55 -2002 728
-5 35 -175 77 -3185 1274 -4998
14 -126 756 -3822 1764 -77112 325584
-42 462 -3234 1848 -94248 447678 -2027718
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