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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 57 |
| 3 | 398 |
| 4 | 2955 |
| 5 | 19158 |
| 6 | 130453 |
| 7 | 820554 |
| 8 | 5280204 |
| 9 | 32711022 |
| 10 | 204324819 |
| 11 | 1249546656 |
| 12 | 7682267669 |
| 13 | 46625705988 |
| 14 | 283766862009 |
| 15 | 1714704081724 |
| 16 | 10374896682273 |
| 17 | 62511439251768 |
| 18 | 376943252871343 |
| 19 | 2267304042230202 |
| 20 | 13643684237963994 |
| 21 | 81983795625450144 |
[1,6,57,398,2955,19158,130453,820554,5280204, 32711022,204324819,1249546656,7682267669, 46625705988,283766862009,1714704081724, 10374896682273,62511439251768,376943252871343, 2267304042230202,13643684237963994, 81983795625450144] |