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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 44 |
| 5 | 308 |
| 6 | 2648 |
| 7 | 26912 |
| 8 | 315536 |
| 9 | 4193744 |
| 10 | 62302496 |
| 11 | 1023057536 |
| 12 | 18400342208 |
| 13 | 359733922880 |
| 14 | 7595810693504 |
| 15 | 172270928222720 |
| 16 | 4176595617747200 |
| 17 | 107793463235860736 |
| 18 | 2950683535353324032 |
| 19 | 85386983313510877184 |
| 20 | 2604521649171407301632 |
| 21 | 83519383797513832420352 |
[1,1,2,8,44,308,2648,26912,315536,4193744, 62302496,1023057536,18400342208,359733922880, 7595810693504,172270928222720,4176595617747200, 107793463235860736,2950683535353324032, 85386983313510877184,2604521649171407301632, 83519383797513832420352] |