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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 13 |
| 6 | 42 |
| 7 | 139 |
| 8 | 506 |
| 9 | 1915 |
| 10 | 7558 |
| 11 | 31092 |
| 12 | 132170 |
| 13 | 580466 |
| 14 | 2624545 |
| 15 | 12190623 |
| 16 | 58083923 |
| 17 | 283346273 |
| 18 | 1413449148 |
| 19 | 7200961616 |
| 20 | 37425264180 |
| 21 | 198239674888 |
| 22 | 1069228024931 |
| 23 | 5867587726222 |
| 24 | 32736878114805 |
| 25 | 185570805235978 |
[0,0,1,2,4,13,42,139,506,1915,7558,31092,132170, 580466,2624545,12190623,58083923,283346273, 1413449148,7200961616,37425264180,198239674888, 1069228024931,5867587726222,32736878114805, 185570805235978] |