The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 104 |
| 5 | 696 |
| 6 | 6272 |
| 7 | 57856 |
| 8 | 652416 |
| 9 | 7657600 |
| 10 | 104244992 |
| 11 | 1475430144 |
| 12 | 23426373632 |
| 13 | 387521615872 |
| 14 | 7034561925120 |
| 15 | 132850810138624 |
| 16 | 2709375373672448 |
| 17 | 57456525327335424 |
| 18 | 1301169515685085184 |
| 19 | 30573796812553584640 |
| 20 | 760486440376336908288 |
| 21 | 19600568102376899608576 |
[1,1,4,16,104,696,6272,57856,652416,7657600, 104244992,1475430144,23426373632,387521615872, 7034561925120,132850810138624,2709375373672448, 57456525327335424,1301169515685085184, 30573796812553584640,760486440376336908288, 19600568102376899608576] |