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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 141 |
| 5 | 986 |
| 6 | 7295 |
| 7 | 56145 |
| 8 | 444900 |
| 9 | 3605429 |
| 10 | 29742671 |
| 11 | 248933630 |
| 12 | 2108590305 |
| 13 | 18042013096 |
| 14 | 155711676129 |
| 15 | 1353913728412 |
| 16 | 11849013783676 |
| 17 | 104293377329508 |
| 18 | 922643326714355 |
| 19 | 8199321046129671 |
| 20 | 73162599757076951 |
[1,1,4,22,141,986,7295,56145,444900,3605429, 29742671,248933630,2108590305,18042013096, 155711676129,1353913728412,11849013783676, 104293377329508,922643326714355,8199321046129671, 73162599757076951] |