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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 7 |
| 4 | 25 |
| 5 | 101 |
| 6 | 721 |
| 7 | 8653 |
| 8 | 66753 |
| 9 | 574489 |
| 10 | 7509601 |
| 11 | 76972281 |
| 12 | 938682625 |
| 13 | 14560953109 |
| 14 | 226747016497 |
| 15 | 4226839991221 |
| 16 | 73582415930881 |
| 17 | 1133352458491185 |
| 18 | 23260378180229569 |
| 19 | 478118972286336241 |
| 20 | 9648062520586144001 |
| 21 | 239696533730926824301 |
| 22 | 6090975028325867045521 |
[1,1,1,7,25,101,721,8653,66753,574489,7509601, 76972281,938682625,14560953109,226747016497, 4226839991221,73582415930881,1133352458491185, 23260378180229569,478118972286336241, 9648062520586144001,239696533730926824301, 6090975028325867045521] |