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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 63 |
| 4 | 1278 |
| 5 | 29764 |
| 6 | 758065 |
| 7 | 20611793 |
| 8 | 590579518 |
| 9 | 17707907024 |
| 10 | 553879330720 |
| 11 | 18066513887790 |
| 12 | 615744470668778 |
| 13 | 22014659625607877 |
| 14 | 830262409494773896 |
| 15 | 33243718957578687811 |
| 16 | 1422095813097928147636 |
| 17 | 65311403344808947050730 |
| 18 | 3227884786251446164710376 |
[1,1,4,63,1278,29764,758065,20611793,590579518, 17707907024,553879330720,18066513887790, 615744470668778,22014659625607877, 830262409494773896,33243718957578687811, 1422095813097928147636,65311403344808947050730, 3227884786251446164710376] |