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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 22 |
| 5 | 147 |
| 6 | 1074 |
| 7 | 8216 |
| 8 | 64798 |
| 9 | 521900 |
| 10 | 4272967 |
| 11 | 35447724 |
| 12 | 297308810 |
| 13 | 2516830890 |
| 14 | 21476307960 |
| 15 | 184530904560 |
| 16 | 1595190209002 |
| 17 | 13863857007924 |
| 18 | 121067796450692 |
| 19 | 1061770618201680 |
| 20 | 9347742325179544 |
| 21 | 82584606893075739 |
[1,1,4,22,147,1074,8216,64798,521900,4272967, 35447724,297308810,2516830890,21476307960, 184530904560,1595190209002,13863857007924, 121067796450692,1061770618201680,9347742325179544, 82584606893075739] |