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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 52 |
| 2 | 1326 |
| 3 | 22100 |
| 4 | 270725 |
| 5 | 2598960 |
| 6 | 20358520 |
| 7 | 133784560 |
| 8 | 752538150 |
| 9 | 3679075400 |
| 10 | 15820024220 |
| 11 | 60403728840 |
| 12 | 206379406870 |
| 13 | 635013559600 |
| 14 | 1768966344600 |
| 15 | 4481381406320 |
| 16 | 10363194502115 |
| 17 | 21945588357420 |
| 18 | 42671977361650 |
| 19 | 76360380541900 |
| 20 | 125994627894135 |
[1,52,1326,22100,270725,2598960,20358520, 133784560,752538150,3679075400,15820024220, 60403728840,206379406870,635013559600, 1768966344600,4481381406320,10363194502115, 21945588357420,42671977361650,76360380541900, 125994627894135] |