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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 66 |
| 3 | 924 |
| 4 | 7400 |
| 5 | 44040 |
| 6 | 217392 |
| 7 | 942592 |
| 8 | 3714048 |
| 9 | 13593600 |
| 10 | 46914560 |
| 11 | 154328064 |
| 12 | 487778304 |
| 13 | 1490384896 |
| 14 | 4423372800 |
| 15 | 12801146880 |
| 16 | 36235378688 |
| 17 | 100580917248 |
| 18 | 274361352192 |
| 19 | 736775372800 |
| 20 | 1950815354880 |
| 21 | 5099601002496 |
| 22 | 13176144920576 |
| 23 | 33682341494784 |
[0,1,66,924,7400,44040,217392,942592,3714048, 13593600,46914560,154328064,487778304,1490384896, 4423372800,12801146880,36235378688,100580917248, 274361352192,736775372800,1950815354880, 5099601002496,13176144920576,33682341494784] |