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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 120 |
| 2 | 9765 |
| 3 | 251680 |
| 4 | 3043425 |
| 5 | 22661496 |
| 6 | 121226245 |
| 7 | 510902400 |
| 8 | 1799118945 |
| 9 | 5507702200 |
| 10 | 15072415941 |
| 11 | 37630041120 |
| 12 | 87029433985 |
| 13 | 188664603960 |
| 14 | 386925380325 |
| 15 | 756298318336 |
| 16 | 1417430759745 |
| 17 | 2559798038520 |
| 18 | 4472991338725 |
| 19 | 7589075296800 |
| 20 | 12538953723681 |
[1,120,9765,251680,3043425,22661496,121226245, 510902400,1799118945,5507702200,15072415941, 37630041120,87029433985,188664603960,386925380325, 756298318336,1417430759745,2559798038520, 4472991338725,7589075296800,12538953723681] |