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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 15 |
| 4 | 104 |
| 5 | 1145 |
| 6 | 13824 |
| 7 | 208831 |
| 8 | 3536000 |
| 9 | 68918769 |
| 10 | 1489702400 |
| 11 | 35742514511 |
| 12 | 937323767808 |
| 13 | 26750313223465 |
| 14 | 824073079660544 |
| 15 | 27276657371589375 |
| 16 | 965004380380626944 |
| 17 | 36347144974616190689 |
| 18 | 1451974448007830568960 |
| 19 | 61319892272079181137679 |
| 20 | 2729671240750270054400000 |
[1,1,2,15,104,1145,13824,208831,3536000,68918769, 1489702400,35742514511,937323767808, 26750313223465,824073079660544,27276657371589375, 965004380380626944,36347144974616190689, 1451974448007830568960,61319892272079181137679, 2729671240750270054400000] |