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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 21 |
| 4 | 80 |
| 5 | 281 |
| 6 | 1138 |
| 7 | 4369 |
| 8 | 18302 |
| 9 | 73789 |
| 10 | 315759 |
| 11 | 1314708 |
| 12 | 5718763 |
| 13 | 24368034 |
| 14 | 107302457 |
| 15 | 464979845 |
| 16 | 2066691614 |
| 17 | 9071525567 |
| 18 | 40625817135 |
| 19 | 180148052526 |
| 20 | 811809392966 |
| 21 | 3629460525990 |
| 22 | 16440663433625 |
| 23 | 73999782874666 |
| 24 | 336685091247671 |
| 25 | 1523982877313501 |
| 26 | 6960274780373417 |
| 27 | 31655866376913556 |
[1,2,7,21,80,281,1138,4369,18302,73789,315759, 1314708,5718763,24368034,107302457,464979845, 2066691614,9071525567,40625817135,180148052526, 811809392966,3629460525990,16440663433625, 73999782874666,336685091247671,1523982877313501, 6960274780373417,31655866376913556] |