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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 0 |
| 4 | 1 |
| 5 | 2 |
| 6 | 9 |
| 7 | 36 |
| 8 | 154 |
| 9 | 668 |
| 10 | 2932 |
| 11 | 13016 |
| 12 | 58364 |
| 13 | 264208 |
| 14 | 1206818 |
| 15 | 5558724 |
| 16 | 25803509 |
| 17 | 120638466 |
| 18 | 567732133 |
| 19 | 2687937916 |
| 20 | 12796823923 |
| 21 | 61235363802 |
| 22 | 294407424869 |
| 23 | 1421635103832 |
| 24 | 6892590800146 |
| 25 | 33543439104796 |
[0,1,0,1,2,9,36,154,668,2932,13016,58364,264208, 1206818,5558724,25803509,120638466,567732133, 2687937916,12796823923,61235363802,294407424869, 1421635103832,6892590800146,33543439104796] |