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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 18 |
| 4 | 112 |
| 5 | 755 |
| 6 | 5348 |
| 7 | 39302 |
| 8 | 296916 |
| 9 | 2291861 |
| 10 | 17997052 |
| 11 | 143319918 |
| 12 | 1154728056 |
| 13 | 9395809374 |
| 14 | 77099733884 |
| 15 | 637298480966 |
| 16 | 5301568498768 |
| 17 | 44351526986704 |
| 18 | 372890978840156 |
| 19 | 3149155955471690 |
| 20 | 26702387443603200 |
| 21 | 227238745573918511 |
| 22 | 1940201017862028108 |
[1,1,3,18,112,755,5348,39302,296916,2291861, 17997052,143319918,1154728056,9395809374, 77099733884,637298480966,5301568498768, 44351526986704,372890978840156,3149155955471690, 26702387443603200,227238745573918511, 1940201017862028108] |