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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 68 |
| 3 | 970 |
| 4 | 15627 |
| 5 | 271698 |
| 6 | 4980320 |
| 7 | 94919382 |
| 8 | 1864060550 |
| 9 | 37486601966 |
| 10 | 768542230128 |
| 11 | 16010270917186 |
| 12 | 338044149765168 |
| 13 | 7220000851821450 |
| 14 | 155743662496011552 |
| 15 | 3388779105788095886 |
| 16 | 74299386925266352272 |
| 17 | 1640069094618726916032 |
| 18 | 36421678762652448251540 |
[1,6,68,970,15627,271698,4980320,94919382, 1864060550,37486601966,768542230128, 16010270917186,338044149765168,7220000851821450, 155743662496011552,3388779105788095886, 74299386925266352272,1640069094618726916032, 36421678762652448251540] |