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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 3 |
| 4 | 16 |
| 5 | 65 |
| 6 | 336 |
| 7 | 1897 |
| 8 | 11824 |
| 9 | 80145 |
| 10 | 586000 |
| 11 | 4588001 |
| 12 | 38239224 |
| 13 | 337611001 |
| 14 | 3144297352 |
| 15 | 30779387745 |
| 16 | 315689119456 |
| 17 | 3383159052833 |
| 18 | 37790736663456 |
| 19 | 439036039824193 |
| 20 | 5294386116882280 |
| 21 | 66155074120062921 |
| 22 | 855156188538926296 |
| 23 | 11418964004032623809 |
[1,0,2,3,16,65,336,1897,11824,80145,586000, 4588001,38239224,337611001,3144297352,30779387745, 315689119456,3383159052833,37790736663456, 439036039824193,5294386116882280, 66155074120062921,855156188538926296, 11418964004032623809] |