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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 44 |
| 3 | 352 |
| 4 | 2940 |
| 5 | 25194 |
| 6 | 219604 |
| 7 | 1937520 |
| 8 | 17250012 |
| 9 | 154663960 |
| 10 | 1394538288 |
| 11 | 12631852688 |
| 12 | 114858935204 |
| 13 | 1047772373340 |
| 14 | 9584557428600 |
| 15 | 87885886492320 |
| 16 | 807564936805020 |
| 17 | 7434289153896264 |
| 18 | 68551275793965328 |
| 19 | 633038816547052800 |
[1,6,44,352,2940,25194,219604,1937520,17250012, 154663960,1394538288,12631852688,114858935204, 1047772373340,9584557428600,87885886492320, 807564936805020,7434289153896264, 68551275793965328,633038816547052800] |