| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 16 |
| 3 | 60 |
| 4 | 256 |
| 5 | 1872 |
| 6 | 15376 |
| 7 | 145200 |
| 8 | 1887876 |
| 9 | 32939236 |
| 10 | 653211364 |
| 11 | 16761239040 |
| 12 | 557862597604 |
| 13 | 24505820603880 |
| 14 | 1374667445474064 |
| 15 | 89177394083197716 |
| 16 | 7769360160391840000 |
| 17 | 912190244879661701508 |
| 18 | 129010731422391263108196 |
[2,16,60,256,1872,15376,145200,1887876,32939236, 653211364,16761239040,557862597604,24505820603880, 1374667445474064,89177394083197716, 7769360160391840000,912190244879661701508, 129010731422391263108196] |