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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 26 |
| 4 | 188 |
| 5 | 1627 |
| 6 | 15172 |
| 7 | 154904 |
| 8 | 1670836 |
| 9 | 18951217 |
| 10 | 222682164 |
| 11 | 2693625128 |
| 12 | 33309537808 |
| 13 | 419311915217 |
| 14 | 5354144473084 |
| 15 | 69169422070152 |
| 16 | 902237854706616 |
| 17 | 11863641066687085 |
| 18 | 157052133090437332 |
| 19 | 2090929291636792824 |
| 20 | 27971914781646817864 |
| 21 | 375725009230868446500 |
[1,1,4,26,188,1627,15172,154904,1670836,18951217, 222682164,2693625128,33309537808,419311915217, 5354144473084,69169422070152,902237854706616, 11863641066687085,157052133090437332, 2090929291636792824,27971914781646817864, 375725009230868446500] |