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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 27 |
| 4 | 292 |
| 5 | 4425 |
| 6 | 89106 |
| 7 | 2280901 |
| 8 | 71928872 |
| 9 | 2728450017 |
| 10 | 122145511510 |
| 11 | 6354868381521 |
| 12 | 379376236939404 |
| 13 | 25710543779239501 |
| 14 | 1960001963705060926 |
| 15 | 166753195643254805565 |
| 16 | 15724259680648667902096 |
| 17 | 1633462474351643785483457 |
| 18 | 185931510605274506452763166 |
[1,1,4,27,292,4425,89106,2280901,71928872, 2728450017,122145511510,6354868381521, 379376236939404,25710543779239501, 1960001963705060926,166753195643254805565, 15724259680648667902096,1633462474351643785483457, 185931510605274506452763166] |