The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 36 |
| 4 | 360 |
| 5 | 2688 |
| 6 | 17280 |
| 7 | 101376 |
| 8 | 559104 |
| 9 | 2949120 |
| 10 | 15040512 |
| 11 | 74711040 |
| 12 | 363331584 |
| 13 | 1736441856 |
| 14 | 8178892800 |
| 15 | 38050725888 |
| 16 | 175154135040 |
| 17 | 798863917056 |
| 18 | 3614214979584 |
| 19 | 16234976378880 |
| 20 | 72464688218112 |
| 21 | 321607151124480 |
[0,2,36,360,2688,17280,101376,559104,2949120, 15040512,74711040,363331584,1736441856,8178892800, 38050725888,175154135040,798863917056, 3614214979584,16234976378880,72464688218112, 321607151124480] |