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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 23 |
| 4 | 233 |
| 5 | 2800 |
| 6 | 42832 |
| 7 | 763220 |
| 8 | 15761709 |
| 9 | 366711200 |
| 10 | 9537738596 |
| 11 | 273549419552 |
| 12 | 8587897407548 |
| 13 | 292755986184548 |
| 14 | 10773140836162944 |
| 15 | 425587704331945152 |
| 16 | 17966341563465800813 |
| 17 | 807152054953801845760 |
| 18 | 38451432814472749509872 |
| 19 | 1936082850634342992601636 |
[1,4,23,233,2800,42832,763220,15761709,366711200, 9537738596,273549419552,8587897407548, 292755986184548,10773140836162944, 425587704331945152,17966341563465800813, 807152054953801845760,38451432814472749509872, 1936082850634342992601636] |