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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 161 |
| 5 | 1321 |
| 6 | 12541 |
| 7 | 130383 |
| 8 | 1482875 |
| 9 | 18153076 |
| 10 | 237430711 |
| 11 | 3295833146 |
| 12 | 48274094584 |
| 13 | 742868875984 |
| 14 | 11963384310515 |
| 15 | 200974595790271 |
| 16 | 3511980095379727 |
| 17 | 63682377891348689 |
| 18 | 1195661594431548085 |
| 19 | 23199930176668566579 |
| 20 | 464421513762097397125 |
| 21 | 9576744471125816269165 |
[1,1,4,22,161,1321,12541,130383,1482875,18153076, 237430711,3295833146,48274094584,742868875984, 11963384310515,200974595790271,3511980095379727, 63682377891348689,1195661594431548085, 23199930176668566579,464421513762097397125, 9576744471125816269165] |