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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 100 |
| 5 | 633 |
| 6 | 4626 |
| 7 | 37878 |
| 8 | 348224 |
| 9 | 3542952 |
| 10 | 39339852 |
| 11 | 478962252 |
| 12 | 6289532928 |
| 13 | 89038853856 |
| 14 | 1346224983936 |
| 15 | 21729308136720 |
| 16 | 371924399416320 |
| 17 | 6740200653419520 |
| 18 | 128878557725067264 |
| 19 | 2598800542616444724 |
| 20 | 54986036469506668800 |
| 21 | 1217069235297874269792 |
[0,1,4,19,100,633,4626,37878,348224,3542952, 39339852,478962252,6289532928,89038853856, 1346224983936,21729308136720,371924399416320, 6740200653419520,128878557725067264, 2598800542616444724,54986036469506668800, 1217069235297874269792] |