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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 20 |
| 4 | 116 |
| 5 | 729 |
| 6 | 4835 |
| 7 | 33308 |
| 8 | 236040 |
| 9 | 1709710 |
| 10 | 12601576 |
| 11 | 94209348 |
| 12 | 712665643 |
| 13 | 5445033052 |
| 14 | 41957720686 |
| 15 | 325702058100 |
| 16 | 2544612673624 |
| 17 | 19993230400674 |
| 18 | 157880283331190 |
| 19 | 1252345341860312 |
| 20 | 9974116387535508 |
| 21 | 79727867712667593 |
| 22 | 639419309923767255 |
| 23 | 5143690907082615272 |
[1,1,4,20,116,729,4835,33308,236040,1709710, 12601576,94209348,712665643,5445033052, 41957720686,325702058100,2544612673624, 19993230400674,157880283331190,1252345341860312, 9974116387535508,79727867712667593, 639419309923767255,5143690907082615272] |