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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 30 |
| 3 | 140 |
| 4 | 630 |
| 5 | 2772 |
| 6 | 12012 |
| 7 | 51480 |
| 8 | 218790 |
| 9 | 923780 |
| 10 | 3879876 |
| 11 | 16224936 |
| 12 | 67603900 |
| 13 | 280816200 |
| 14 | 1163381400 |
| 15 | 4808643120 |
| 16 | 19835652870 |
| 17 | 81676217700 |
| 18 | 335780006100 |
| 19 | 1378465288200 |
| 20 | 5651707681620 |
| 21 | 23145088600920 |
| 22 | 94684453367400 |
| 23 | 386971244197200 |
| 24 | 1580132580471900 |
[1,6,30,140,630,2772,12012,51480,218790,923780, 3879876,16224936,67603900,280816200,1163381400, 4808643120,19835652870,81676217700,335780006100, 1378465288200,5651707681620,23145088600920, 94684453367400,386971244197200,1580132580471900] |