The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 60 |
| 5 | 276 |
| 6 | 1248 |
| 7 | 6816 |
| 8 | 36960 |
| 9 | 236160 |
| 10 | 1503360 |
| 11 | 11041920 |
| 12 | 80922240 |
| 13 | 672779520 |
| 14 | 5585448960 |
| 15 | 51894743040 |
| 16 | 481684008960 |
| 17 | 4948521984000 |
| 18 | 50802038784000 |
| 19 | 571990616064000 |
| 20 | 6436746860544000 |
| 21 | 78834313248768000 |
| 22 | 965131970052096000 |
[1,4,16,60,276,1248,6816,36960,236160,1503360, 11041920,80922240,672779520,5585448960, 51894743040,481684008960,4948521984000, 50802038784000,571990616064000,6436746860544000, 78834313248768000,965131970052096000] |