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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 15 |
| 2 | 120 |
| 3 | 695 |
| 4 | 3285 |
| 5 | 13443 |
| 6 | 49305 |
| 7 | 165795 |
| 8 | 519240 |
| 9 | 1531960 |
| 10 | 4295046 |
| 11 | 11520000 |
| 12 | 29718605 |
| 13 | 74060355 |
| 14 | 178930605 |
| 15 | 420368858 |
| 16 | 962785560 |
| 17 | 2154411120 |
| 18 | 4718952965 |
| 19 | 10134292275 |
| 20 | 21369644184 |
| 21 | 44300604895 |
| 22 | 90390209685 |
| 23 | 181706747280 |
| 24 | 360207189225 |
| 25 | 704726281002 |
| 26 | 1361748557400 |
[1,15,120,695,3285,13443,49305,165795,519240, 1531960,4295046,11520000,29718605,74060355, 178930605,420368858,962785560,2154411120, 4718952965,10134292275,21369644184,44300604895, 90390209685,181706747280,360207189225, 704726281002,1361748557400] |