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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 26 |
| 4 | 234 |
| 5 | 2694 |
| 6 | 37812 |
| 7 | 626352 |
| 8 | 11962164 |
| 9 | 258787812 |
| 10 | 6255195168 |
| 11 | 167072685240 |
| 12 | 4886611129320 |
| 13 | 155335056242040 |
| 14 | 5332298685827760 |
| 15 | 196590247328769120 |
| 16 | 7747254471910795920 |
| 17 | 324986515253994589200 |
| 18 | 14458392906960271354560 |
| 19 | 679977065168639138610720 |
[1,1,4,26,234,2694,37812,626352,11962164, 258787812,6255195168,167072685240,4886611129320, 155335056242040,5332298685827760, 196590247328769120,7747254471910795920, 324986515253994589200,14458392906960271354560, 679977065168639138610720] |