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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 15 |
| 3 | 143 |
| 4 | 1069 |
| 5 | 9612 |
| 6 | 82634 |
| 7 | 707903 |
| 8 | 6155230 |
| 9 | 53074167 |
| 10 | 458901955 |
| 11 | 3968548571 |
| 12 | 34293794622 |
| 13 | 296497719200 |
| 14 | 2563023778341 |
| 15 | 22155553744380 |
| 16 | 191528023181443 |
| 17 | 1655649630655481 |
| 18 | 14312296720331975 |
| 19 | 123722938782920490 |
| 20 | 1069522524403416934 |
| 21 | 9245501816227527991 |
[1,2,15,143,1069,9612,82634,707903,6155230, 53074167,458901955,3968548571,34293794622, 296497719200,2563023778341,22155553744380, 191528023181443,1655649630655481, 14312296720331975,123722938782920490, 1069522524403416934,9245501816227527991] |