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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 30 |
| 3 | 276 |
| 4 | 2825 |
| 5 | 30884 |
| 6 | 353108 |
| 7 | 4170500 |
| 8 | 50485764 |
| 9 | 623084056 |
| 10 | 7810707894 |
| 11 | 99175174284 |
| 12 | 1272856327470 |
| 13 | 16486135484248 |
| 14 | 215212582153840 |
| 15 | 2828658852385572 |
| 16 | 37401956484705132 |
| 17 | 497174193516767600 |
| 18 | 6640063367021736728 |
| 19 | 89058042321373540912 |
| 20 | 1199031374607501831273 |
[1,4,30,276,2825,30884,353108,4170500,50485764, 623084056,7810707894,99175174284,1272856327470, 16486135484248,215212582153840,2828658852385572, 37401956484705132,497174193516767600, 6640063367021736728,89058042321373540912, 1199031374607501831273] |