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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 7 |
| 3 | 43 |
| 4 | 259 |
| 5 | 1555 |
| 6 | 9331 |
| 7 | 55987 |
| 8 | 335923 |
| 9 | 2015539 |
| 10 | 12093235 |
| 11 | 72559411 |
| 12 | 435356467 |
| 13 | 2612138803 |
| 14 | 15672832819 |
| 15 | 94036996915 |
| 16 | 564221981491 |
| 17 | 3385331888947 |
| 18 | 20311991333683 |
| 19 | 121871948002099 |
| 20 | 731231688012595 |
| 21 | 4387390128075571 |
[0,1,7,43,259,1555,9331,55987,335923,2015539, 12093235,72559411,435356467,2612138803, 15672832819,94036996915,564221981491, 3385331888947,20311991333683,121871948002099, 731231688012595,4387390128075571] |