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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 102 |
| 4 | 870 |
| 5 | 8892 |
| 6 | 105708 |
| 7 | 1431168 |
| 8 | 21722136 |
| 9 | 365105928 |
| 10 | 6729341832 |
| 11 | 134915992560 |
| 12 | 2922576142320 |
| 13 | 68013701197920 |
| 14 | 1692075061072800 |
| 15 | 44810389419079680 |
| 16 | 1258472984174461440 |
| 17 | 37357062009383877120 |
| 18 | 1168635883239630120960 |
| 19 | 38424619272539153157120 |
[1,3,15,102,870,8892,105708,1431168,21722136, 365105928,6729341832,134915992560,2922576142320, 68013701197920,1692075061072800,44810389419079680, 1258472984174461440,37357062009383877120, 1168635883239630120960,38424619272539153157120] |