| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 26 |
| 4 | 240 |
| 5 | 2882 |
| 6 | 42560 |
| 7 | 745418 |
| 8 | 15097600 |
| 9 | 347066882 |
| 10 | 8926258176 |
| 11 | 253930611002 |
| 12 | 7916100448256 |
| 13 | 268352394448322 |
| 14 | 9828088361009152 |
| 15 | 386707997366768618 |
| 16 | 16268790735900180480 |
| 17 | 728714136550643404802 |
| 18 | 34624041592426892361728 |
[2,4,26,240,2882,42560,745418,15097600,347066882, 8926258176,253930611002,7916100448256, 268352394448322,9828088361009152, 386707997366768618,16268790735900180480, 728714136550643404802,34624041592426892361728] |