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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 17 |
| 7 | 80 |
| 8 | 422 |
| 9 | 2480 |
| 10 | 16095 |
| 11 | 114432 |
| 12 | 884969 |
| 13 | 7398464 |
| 14 | 66502048 |
| 15 | 639653632 |
| 16 | 6556170841 |
| 17 | 71340409600 |
| 18 | 821408397105 |
| 19 | 9977630263296 |
| 20 | 127518757153174 |
| 21 | 1710576547456000 |
| 22 | 24030971882538671 |
| 23 | 352843606806499328 |
[1,1,0,0,1,4,17,80,422,2480,16095,114432,884969, 7398464,66502048,639653632,6556170841,71340409600, 821408397105,9977630263296,127518757153174, 1710576547456000,24030971882538671, 352843606806499328] |