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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 16 |
| 4 | 126 |
| 5 | 1296 |
| 6 | 16071 |
| 7 | 228514 |
| 8 | 3607890 |
| 9 | 61891050 |
| 10 | 1135871490 |
| 11 | 22049362440 |
| 12 | 448790912004 |
| 13 | 9512960347260 |
| 14 | 208858963314735 |
| 15 | 4728736078065810 |
| 16 | 110006925920592810 |
| 17 | 2621619942885055530 |
| 18 | 63840054782606886630 |
| 19 | 1585094577104979776880 |
| 20 | 40054740803371374834780 |
| 21 | 1028483346608802276173280 |
[1,1,3,16,126,1296,16071,228514,3607890,61891050, 1135871490,22049362440,448790912004,9512960347260, 208858963314735,4728736078065810, 110006925920592810,2621619942885055530, 63840054782606886630,1585094577104979776880, 40054740803371374834780,1028483346608802276173280] |