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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 177 |
| 5 | 1462 |
| 6 | 21919 |
| 7 | 254802 |
| 8 | 4816788 |
| 9 | 82401465 |
| 10 | 1929926410 |
| 11 | 35256890748 |
| 12 | 1152938630784 |
| 13 | 24977973856643 |
| 14 | 823036511854847 |
| 15 | 24332827884557037 |
| 16 | 954801492779273665 |
| 17 | 27023410818058291822 |
| 18 | 1309814517293654535339 |
| 19 | 41375530521928893861920 |
[1,1,4,20,177,1462,21919,254802,4816788,82401465, 1929926410,35256890748,1152938630784, 24977973856643,823036511854847,24332827884557037, 954801492779273665,27023410818058291822, 1309814517293654535339,41375530521928893861920] |