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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 67 |
| 5 | 457 |
| 6 | 3734 |
| 7 | 35741 |
| 8 | 392875 |
| 9 | 4886114 |
| 10 | 67924417 |
| 11 | 1044531625 |
| 12 | 17609980356 |
| 13 | 322993544751 |
| 14 | 6402464186243 |
| 15 | 136373115537072 |
| 16 | 3105809328600351 |
| 17 | 75300018326324541 |
| 18 | 1936106590359322126 |
| 19 | 52615058519875702993 |
| 20 | 1506721174739412743551 |
[1,1,3,12,67,457,3734,35741,392875,4886114, 67924417,1044531625,17609980356,322993544751, 6402464186243,136373115537072,3105809328600351, 75300018326324541,1936106590359322126, 52615058519875702993,1506721174739412743551] |