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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 26 |
| 4 | 254 |
| 5 | 3538 |
| 6 | 67014 |
| 7 | 1660866 |
| 8 | 52230550 |
| 9 | 2033261906 |
| 10 | 96018823814 |
| 11 | 5409008246626 |
| 12 | 358368831222006 |
| 13 | 27589872391918194 |
| 14 | 2442595357421865574 |
| 15 | 246430234111929035906 |
| 16 | 28106918525950072081622 |
| 17 | 3598669462582938225587602 |
| 18 | 513978991104098010878849094 |
[1,1,4,26,254,3538,67014,1660866,52230550, 2033261906,96018823814,5409008246626, 358368831222006,27589872391918194, 2442595357421865574,246430234111929035906, 28106918525950072081622,3598669462582938225587602, 513978991104098010878849094] |