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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 26 |
| 4 | 107 |
| 5 | 486 |
| 6 | 2398 |
| 7 | 12668 |
| 8 | 70863 |
| 9 | 416304 |
| 10 | 2552490 |
| 11 | 16254406 |
| 12 | 107095090 |
| 13 | 727834866 |
| 14 | 5089682472 |
| 15 | 36548625188 |
| 16 | 269065010063 |
| 17 | 2027942075946 |
| 18 | 15630423416331 |
| 19 | 123079853443384 |
| 20 | 989356860469923 |
| 21 | 8112792202324232 |
[1,2,7,26,107,486,2398,12668,70863,416304,2552490, 16254406,107095090,727834866,5089682472, 36548625188,269065010063,2027942075946, 15630423416331,123079853443384,989356860469923, 8112792202324232] |