The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 16 |
| 3 | 144 |
| 4 | 960 |
| 5 | 12880 |
| 6 | 62208 |
| 7 | 1087632 |
| 8 | 7027200 |
| 9 | 85098816 |
| 10 | 691398400 |
| 11 | 10374307328 |
| 12 | 49985372160 |
| 13 | 1061265441600 |
| 14 | 7064952935040 |
| 15 | 90426613939200 |
| 16 | 708867057254400 |
| 17 | 11892871258806912 |
| 18 | 65078340559220736 |
| 19 | 1287559798913990448 |
| 20 | 8819554320783360000 |
| 21 | 111715065087913437696 |
[4,16,144,960,12880,62208,1087632,7027200, 85098816,691398400,10374307328,49985372160, 1061265441600,7064952935040,90426613939200, 708867057254400,11892871258806912, 65078340559220736,1287559798913990448, 8819554320783360000,111715065087913437696] |