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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 202 |
| 5 | 1944 |
| 6 | 21356 |
| 7 | 261213 |
| 8 | 3500132 |
| 9 | 50800750 |
| 10 | 791987356 |
| 11 | 13177143096 |
| 12 | 232770367228 |
| 13 | 4346862352088 |
| 14 | 85504298103304 |
| 15 | 1766037126815893 |
| 16 | 38195654668499866 |
| 17 | 862911190841993448 |
| 18 | 20318964099125136372 |
[1,1,4,25,202,1944,21356,261213,3500132,50800750, 791987356,13177143096,232770367228,4346862352088, 85504298103304,1766037126815893,38195654668499866, 862911190841993448,20318964099125136372] |