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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 218 |
| 5 | 2451 |
| 6 | 33832 |
| 7 | 554527 |
| 8 | 10535100 |
| 9 | 227790505 |
| 10 | 5525843696 |
| 11 | 148673435769 |
| 12 | 4394818486456 |
| 13 | 141611317636075 |
| 14 | 4940870266568160 |
| 15 | 185595910032346111 |
| 16 | 7468517348971708688 |
| 17 | 320562141349559055633 |
| 18 | 14619577651630443611200 |
| 19 | 706025600924216704982425 |
[1,1,4,25,218,2451,33832,554527,10535100, 227790505,5525843696,148673435769,4394818486456, 141611317636075,4940870266568160, 185595910032346111,7468517348971708688, 320562141349559055633,14619577651630443611200, 706025600924216704982425] |