Pyramid #976
Generating function
$$U_{976}(x, y) = \frac{2 \sqrt{3} \sin{\left(\frac{\operatorname{asin}{\left(\frac{3 \sqrt{3} \sqrt{x \left(y + 1\right)}}{2} \right)}}{3} \right)}}{3 \sqrt{x \left(y + 1\right)}}$$
Explicit formula
$$Tsqrt(n, k) = \begin{cases}\binom{m}{n} 4^{n}&\text{if k even, where m =} \frac{k} {2},\\\frac {{(-1)}^{n-m} \binom{n}{m} \binom{2n}{n}} {\binom{2n}{2m}} &\text{if k odd, n > m, where m =} \frac{k+1} {2},\\\frac {\binom{2m}{2n} \binom{2n}{n}} {\binom{m}{n}}&\text{if k odd, n} \le \text{m, where m =} \frac{k+1} {2},\\\end{cases} $$$$T_{976}(n, m, k) = \frac{k \operatorname{Tsqrt}{\left(m,n \right)} {\binom{k + 3 n - 1}{n}}}{k + 2 n}$$
Data table
1 0 0 0 0 0 0
1 2 -2 4 -10 28 -84
3 12 0 0 0 0 0
12 72 72 -48 72 -144 336
55 440 88 0 0 0 0
273 2730 8190 546 -2730 3276 -5460
1428 17136 68544 91392 0 0 0
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