Generating function
$$U_{91}(x, y) = \frac{x + y}{\left(- x - y + 1\right)^{2}}$$
Explicit formula
$$T_{91}(n, m, k) = {\binom{m + n}{m}} {\binom{k + m + n - 1}{- k + m + n}}$$
| 0 | 1 | 2 | 3 | 4 | 5 | 6 |
| 1 | 4 | 9 | 16 | 25 | 36 | 49 |
| 2 | 9 | 24 | 5 | 9 | 147 | 224 |
| 3 | 16 | 5 | 12 | 245 | 448 | 756 |
| 4 | 25 | 9 | 245 | 56 | 1134 | 21 |
| 5 | 36 | 147 | 448 | 1134 | 252 | 5082 |
| 6 | 49 | 224 | 756 | 21 | 5082 | 11088 |
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