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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 20 |
| 4 | 234 |
| 5 | 4159 |
| 6 | 101538 |
| 7 | 3182454 |
| 8 | 122285201 |
| 9 | 5575750271 |
| 10 | 294529785168 |
| 11 | 17697480642005 |
| 12 | 1192398100081202 |
| 13 | 89053864927236146 |
| 14 | 7302988011333915878 |
| 15 | 652439391227186881683 |
| 16 | 63077327237347821501754 |
| 17 | 6561701255914880362990927 |
| 18 | 730833849063629052249986940 |
[1,1,3,20,234,4159,101538,3182454,122285201, 5575750271,294529785168,17697480642005, 1192398100081202,89053864927236146, 7302988011333915878,652439391227186881683, 63077327237347821501754,6561701255914880362990927, 730833849063629052249986940] |