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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 263 |
| 5 | 5566 |
| 6 | 239428 |
| 7 | 21074412 |
| 8 | 3779440490 |
| 9 | 1372163701412 |
| 10 | 1003687569555456 |
| 11 | 1474604145003923000 |
| 12 | 4343524388729516494384 |
| 13 | 25623424478746329214500144 |
| 14 | 302549202766446393276528844768 |
| 15 | 7147753721248229224770005386691680 |
[1,1,4,24,263,5566,239428,21074412,3779440490, 1372163701412,1003687569555456, 1474604145003923000,4343524388729516494384, 25623424478746329214500144, 302549202766446393276528844768, 7147753721248229224770005386691680] |