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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 40 |
| 4 | 254 |
| 5 | 1868 |
| 6 | 15996 |
| 7 | 153144 |
| 8 | 1637520 |
| 9 | 19191072 |
| 10 | 245463936 |
| 11 | 3390905472 |
| 12 | 50406479328 |
| 13 | 800678811840 |
| 14 | 13547088596544 |
| 15 | 242995426574976 |
| 16 | 4607744279916672 |
| 17 | 92046384885051648 |
| 18 | 1932579234508861440 |
| 19 | 42530614791735573504 |
| 20 | 979132781170084872960 |
| 21 | 23529915213836747927040 |
[1,2,8,40,254,1868,15996,153144,1637520,19191072, 245463936,3390905472,50406479328,800678811840, 13547088596544,242995426574976,4607744279916672, 92046384885051648,1932579234508861440, 42530614791735573504,979132781170084872960, 23529915213836747927040] |