Pyramid #604
Generating function
$$U_{604}(x, y) = \frac{\sqrt{4 x + \frac{\left(\sqrt{4 y + 1} + 1\right)^{4}}{16}} + \frac{\left(\sqrt{4 y + 1} + 1\right)^{2}}{4}}{\sqrt{4 y + 1} + 1}$$
Explicit formula
$$T_{604}(n, m, k) = \begin{cases}1&\text{if m=0,n=0} ,\ \\\frac{\left(-1\right)^{m - 1} \left(k - 4 n\right) {\binom{- k + 2 m + 4 n - 1}{m - 1}}}{m}&\text{if n = 0,m > 0} ,\ \\\frac{\left(-1\right)^{m - 1} k \left(k - 4 n\right) {\binom{k - n - 1}{n - 1}} {\binom{- k + 2 m + 4 n - 1}{m - 1}}}{m n}&\text{if n > 0,m > 0} ,\ \\\frac{k {\binom{k - n - 1}{n - 1}}}{n}&\text{if m = 0,n > 0} \end{cases} $$
Data table
1 1 -1 2 -5 14 -42
1 -3 9 -28 9 -297 1001
-1 7 -35 154 -637 2548 -9996
2 -22 154 -88 4488 -21318 96558
-5 75 -675 475 -28875 15939 -82225
14 -266 2926 -24472 1729 -108927 6317766
-42 966 -12558 121716 -98049 6947472 -44799216
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