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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 8 |
| 5 | 44 |
| 6 | 288 |
| 7 | 2172 |
| 8 | 18516 |
| 9 | 175352 |
| 10 | 1819868 |
| 11 | 20491844 |
| 12 | 248417128 |
| 13 | 3221797252 |
| 14 | 44464876996 |
| 15 | 650076797232 |
| 16 | 10028658649668 |
| 17 | 162695157490644 |
| 18 | 2767333692834768 |
| 19 | 49221196196394252 |
| 20 | 913310582666986596 |
[1,1,2,8,44,288,2172,18516,175352,1819868, 20491844,248417128,3221797252,44464876996, 650076797232,10028658649668,162695157490644, 2767333692834768,49221196196394252, 913310582666986596] |