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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 8 |
| 5 | 52 |
| 6 | 480 |
| 7 | 5811 |
| 8 | 87768 |
| 9 | 1599189 |
| 10 | 34317476 |
| 11 | 851848787 |
| 12 | 24117965057 |
| 13 | 770085965621 |
| 14 | 27472955220394 |
| 15 | 1086491917437511 |
| 16 | 47313129973804599 |
| 17 | 2255470786017010440 |
| 18 | 117103678748934306726 |
| 19 | 6591945250191262271448 |
| 20 | 400690880212910627734513 |
| 21 | 26204671530683391316131317 |
[1,1,2,8,52,480,5811,87768,1599189,34317476, 851848787,24117965057,770085965621,27472955220394, 1086491917437511,47313129973804599, 2255470786017010440,117103678748934306726, 6591945250191262271448,400690880212910627734513, 26204671530683391316131317] |