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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 36 |
| 4 | 251 |
| 5 | 1891 |
| 6 | 15007 |
| 7 | 123593 |
| 8 | 1046444 |
| 9 | 9052330 |
| 10 | 79660406 |
| 11 | 710879890 |
| 12 | 6418000050 |
| 13 | 58515227946 |
| 14 | 538008396198 |
| 15 | 4982752630656 |
| 16 | 46442071874398 |
| 17 | 435299781856712 |
| 18 | 4100411743983559 |
| 19 | 38797120485576155 |
| 20 | 368561495153257186 |
| 21 | 3513923237883474314 |
[1,1,6,36,251,1891,15007,123593,1046444,9052330, 79660406,710879890,6418000050,58515227946, 538008396198,4982752630656,46442071874398, 435299781856712,4100411743983559, 38797120485576155,368561495153257186, 3513923237883474314] |