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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 114 |
| 5 | 703 |
| 6 | 4565 |
| 7 | 30752 |
| 8 | 212921 |
| 9 | 1505916 |
| 10 | 10833164 |
| 11 | 79018804 |
| 12 | 583062388 |
| 13 | 4344431508 |
| 14 | 32641910199 |
| 15 | 247033970128 |
| 16 | 1881402836376 |
| 17 | 14408753414558 |
| 18 | 110897147057354 |
| 19 | 857307054338476 |
| 20 | 6653979156676983 |
| 21 | 51831065993122915 |
| 22 | 405060413133136902 |
| 23 | 3175019470333290488 |
[1,1,4,20,114,703,4565,30752,212921,1505916, 10833164,79018804,583062388,4344431508, 32641910199,247033970128,1881402836376, 14408753414558,110897147057354,857307054338476, 6653979156676983,51831065993122915, 405060413133136902,3175019470333290488] |