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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 21 |
| 3 | 228 |
| 4 | 1733 |
| 5 | 14277 |
| 6 | 110506 |
| 7 | 870027 |
| 8 | 6717882 |
| 9 | 52248430 |
| 10 | 404872294 |
| 11 | 3137029417 |
| 12 | 24306328888 |
| 13 | 188293396538 |
| 14 | 1458607561162 |
| 15 | 11298886140485 |
| 16 | 87523428512115 |
| 17 | 677973532822056 |
| 18 | 5251692364017630 |
| 19 | 40680417109724197 |
| 20 | 315116602409454269 |
[1,21,228,1733,14277,110506,870027,6717882, 52248430,404872294,3137029417,24306328888, 188293396538,1458607561162,11298886140485, 87523428512115,677973532822056,5251692364017630, 40680417109724197,315116602409454269] |