| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 55 |
| 4 | 376 |
| 5 | 3649 |
| 6 | 29260 |
| 7 | 259351 |
| 8 | 2178544 |
| 9 | 18828865 |
| 10 | 160278676 |
| 11 | 1375440439 |
| 12 | 11752630120 |
| 13 | 100652697601 |
| 14 | 860963365084 |
| 15 | 7369308666775 |
| 16 | 63054805905376 |
| 17 | 539622261625729 |
| 18 | 4617626476812580 |
| 19 | 39515774110653751 |
| 20 | 338150529038305624 |
| 21 | 2893717306468718785 |
[0,1,4,55,376,3649,29260,259351,2178544,18828865, 160278676,1375440439,11752630120,100652697601, 860963365084,7369308666775,63054805905376, 539622261625729,4617626476812580, 39515774110653751,338150529038305624, 2893717306468718785] |