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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 131 |
| 5 | 1136 |
| 6 | 11670 |
| 7 | 138727 |
| 8 | 1864711 |
| 9 | 27843874 |
| 10 | 456081803 |
| 11 | 8114074563 |
| 12 | 155519173031 |
| 13 | 3189879446235 |
| 14 | 69629136671356 |
| 15 | 1609836360587087 |
| 16 | 39262941548917619 |
| 17 | 1006616998791629666 |
| 18 | 27044968746461571213 |
[1,1,4,19,131,1136,11670,138727,1864711,27843874, 456081803,8114074563,155519173031,3189879446235, 69629136671356,1609836360587087,39262941548917619, 1006616998791629666,27044968746461571213] |