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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 20 |
| 5 | 52 |
| 6 | 357 |
| 7 | 935 |
| 8 | 6408 |
| 9 | 16776 |
| 10 | 114985 |
| 11 | 301035 |
| 12 | 2063324 |
| 13 | 5401852 |
| 14 | 37024845 |
| 15 | 96932303 |
| 16 | 664383888 |
| 17 | 1739379600 |
| 18 | 11921885137 |
| 19 | 31211900499 |
| 20 | 213929548580 |
| 21 | 560074829380 |
| 22 | 3838809989301 |
| 23 | 10050135028343 |
| 24 | 68884650258840 |
| 25 | 180342355680792 |
| 26 | 1236084894669817 |
[0,1,3,20,52,357,935,6408,16776,114985,301035, 2063324,5401852,37024845,96932303,664383888, 1739379600,11921885137,31211900499,213929548580, 560074829380,3838809989301,10050135028343, 68884650258840,180342355680792,1236084894669817] |