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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 30 |
| 3 | 246 |
| 4 | 2037 |
| 5 | 16886 |
| 6 | 139997 |
| 7 | 1160693 |
| 8 | 9623140 |
| 9 | 79784098 |
| 10 | 661478734 |
| 11 | 5484227157 |
| 12 | 45468956106 |
| 13 | 376976720745 |
| 14 | 3125460977225 |
| 15 | 25912757426660 |
| 16 | 214839027697334 |
| 17 | 1781200165693270 |
| 18 | 14767680082482085 |
| 19 | 122436758775876478 |
[1,4,30,246,2037,16886,139997,1160693,9623140, 79784098,661478734,5484227157,45468956106, 376976720745,3125460977225,25912757426660, 214839027697334,1781200165693270, 14767680082482085,122436758775876478] |