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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 840 |
| 2 | 95802 |
| 3 | 3504816 |
| 4 | 55350120 |
| 5 | 465944304 |
| 6 | 2610853840 |
| 7 | 11337146784 |
| 8 | 40208417466 |
| 9 | 123411903160 |
| 10 | 335056780464 |
| 11 | 830096613360 |
| 12 | 1893781702512 |
| 13 | 4058779021584 |
| 14 | 8190877926720 |
| 15 | 15805879161632 |
| 16 | 29122237029480 |
| 17 | 51905458442208 |
| 18 | 89163973663338 |
| 19 | 149313692762640 |
| 20 | 242598110651568 |
[1,840,95802,3504816,55350120,465944304, 2610853840,11337146784,40208417466,123411903160, 335056780464,830096613360,1893781702512, 4058779021584,8190877926720,15805879161632, 29122237029480,51905458442208,89163973663338, 149313692762640,242598110651568] |