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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 106 |
| 5 | 975 |
| 6 | 11106 |
| 7 | 151501 |
| 8 | 2415960 |
| 9 | 44221869 |
| 10 | 915826600 |
| 11 | 21211128411 |
| 12 | 544126606992 |
| 13 | 15334985416075 |
| 14 | 471495297242256 |
| 15 | 15719617534811625 |
| 16 | 565271886957356416 |
| 17 | 21820620411482896089 |
| 18 | 900398349688515500160 |
| 19 | 39564926462522623540519 |
| 20 | 1845034125763359894240000 |
[1,1,3,15,106,975,11106,151501,2415960,44221869, 915826600,21211128411,544126606992,15334985416075, 471495297242256,15719617534811625, 565271886957356416,21820620411482896089, 900398349688515500160,39564926462522623540519, 1845034125763359894240000] |