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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 21 |
| 3 | 175 |
| 4 | 1185 |
| 5 | 7471 |
| 6 | 45801 |
| 7 | 277495 |
| 8 | 1672545 |
| 9 | 10056991 |
| 10 | 60405081 |
| 11 | 362615815 |
| 12 | 2176242705 |
| 13 | 13059083311 |
| 14 | 78359348361 |
| 15 | 470170570135 |
| 16 | 2821066729665 |
| 17 | 16926530042431 |
| 18 | 101559568723641 |
| 19 | 609358576700455 |
| 20 | 3656154951181425 |
[0,1,21,175,1185,7471,45801,277495,1672545, 10056991,60405081,362615815,2176242705, 13059083311,78359348361,470170570135, 2821066729665,16926530042431,101559568723641, 609358576700455,3656154951181425] |