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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 118 |
| 5 | 886 |
| 6 | 7786 |
| 7 | 78184 |
| 8 | 881644 |
| 9 | 11017108 |
| 10 | 150966856 |
| 11 | 2249261356 |
| 12 | 36181351504 |
| 13 | 624658612384 |
| 14 | 11516406883528 |
| 15 | 225740649754936 |
| 16 | 4686671645814736 |
| 17 | 102712289940757264 |
| 18 | 2369128149877075264 |
| 19 | 57359541280704038128 |
| 20 | 1454229915957292684576 |
[1,1,4,19,118,886,7786,78184,881644,11017108, 150966856,2249261356,36181351504,624658612384, 11516406883528,225740649754936,4686671645814736, 102712289940757264,2369128149877075264, 57359541280704038128,1454229915957292684576] |