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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 20 |
| 3 | 169 |
| 4 | 1667 |
| 5 | 18084 |
| 6 | 208960 |
| 7 | 2527074 |
| 8 | 31630390 |
| 9 | 406680465 |
| 10 | 5342750699 |
| 11 | 71442850111 |
| 12 | 969548468960 |
| 13 | 13323571588607 |
| 14 | 185072895183632 |
| 15 | 2594890728951909 |
| 16 | 36681505784903758 |
| 17 | 522291180086851188 |
| 18 | 7484621370716999785 |
| 19 | 107876522368295972285 |
| 20 | 1562916545414144667559 |
[1,3,20,169,1667,18084,208960,2527074,31630390, 406680465,5342750699,71442850111,969548468960, 13323571588607,185072895183632,2594890728951909, 36681505784903758,522291180086851188, 7484621370716999785,107876522368295972285, 1562916545414144667559] |