Generating function
$$U_{1121}(x, y) = \left(\frac{x}{1 - y} + 1\right)^{3}$$
Explicit formula
$$T_{1121}(n, m, k) = {\binom{3 k}{n}} {\binom{m + n - 1}{m}}$$
| 1 | 0 | 0 | 0 | 0 | 0 | 0 |
| 3 | 3 | 3 | 3 | 3 | 3 | 3 |
| 3 | 6 | 9 | 12 | 15 | 18 | 21 |
| 1 | 3 | 6 | 1 | 15 | 21 | 28 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 0 | 0 | 0 | 0 | 0 | 0 | 0 |
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