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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 51 |
| 4 | 531 |
| 5 | 6331 |
| 6 | 83532 |
| 7 | 1195452 |
| 8 | 18316582 |
| 9 | 297727712 |
| 10 | 5099398853 |
| 11 | 91554269703 |
| 12 | 1715910362408 |
| 13 | 33457504204403 |
| 14 | 676778172939139 |
| 15 | 14168046060375184 |
| 16 | 306327815585165519 |
| 17 | 6827996259530724139 |
| 18 | 156654003923243040925 |
| 19 | 3694188118839057258940 |
| 20 | 89428870506038692255920 |
[1,1,6,51,531,6331,83532,1195452,18316582, 297727712,5099398853,91554269703,1715910362408, 33457504204403,676778172939139,14168046060375184, 306327815585165519,6827996259530724139, 156654003923243040925,3694188118839057258940, 89428870506038692255920] |