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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 18 |
| 5 | 45 |
| 6 | 360 |
| 7 | 1575 |
| 8 | 20790 |
| 9 | 99225 |
| 10 | 1332450 |
| 11 | 9823275 |
| 12 | 181496700 |
| 13 | 1404728325 |
| 14 | 26221595400 |
| 15 | 273922023375 |
| 16 | 7196040101250 |
| 17 | 69850115960625 |
| 18 | 1662139682453250 |
| 19 | 22561587455281875 |
| 20 | 675158520854317500 |
| 21 | 9002073394657468125 |
| 22 | 259715927440434465000 |
[1,1,2,3,18,45,360,1575,20790,99225,1332450, 9823275,181496700,1404728325,26221595400, 273922023375,7196040101250,69850115960625, 1662139682453250,22561587455281875, 675158520854317500,9002073394657468125, 259715927440434465000] |