Generating function
$$U_{1067}(x, y) = \frac{\left(1 - \sqrt{1 - 4 x}\right)^{3}}{8 x^{3} \left(1 - y\right)^{3}}$$
Explicit formula
$$T_{1067}(n, m, k) = \frac{3 k {\binom{3 k + m - 1}{m}} {\binom{3 k + 2 n - 1}{n}}}{3 k + n}$$
Data table
1 3 6 1 15 21 28
3 9 18 3 45 63 84
9 27 54 9 135 189 252
28 84 168 28 42 588 784
9 27 54 9 135 189 252
297 891 1782 297 4455 6237 8316
1001 3003 6006 1001 15015 21021 28028
Export
expand_less