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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 3 |
| 4 | 13 |
| 5 | 53 |
| 6 | 2906 |
| 7 | 30391 |
| 8 | 306356 |
| 9 | 1544521 |
| 10 | 314487775 |
| 11 | 5311670611 |
| 12 | 71438659315 |
| 13 | 8643791799805 |
| 14 | 208502988236908 |
| 15 | 4525624184096751 |
| 16 | 55200677713457866 |
| 17 | 15583522643116493073 |
| 18 | 466115766638709659105 |
| 19 | 11099251895486710352779 |
| 20 | 1358250003379776429113 |
| 21 | 75419018385982521381124421 |
[1,0,3,13,53,2906,30391,306356,1544521,314487775, 5311670611,71438659315,8643791799805, 208502988236908,4525624184096751, 55200677713457866,15583522643116493073, 466115766638709659105,11099251895486710352779, 1358250003379776429113,75419018385982521381124421] |