The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 10 |
| 4 | 40 |
| 5 | 168 |
| 6 | 1008 |
| 7 | 7920 |
| 8 | 63360 |
| 9 | 570240 |
| 10 | 5080320 |
| 11 | 47174400 |
| 12 | 566092800 |
| 13 | 8143027200 |
| 14 | 114002380800 |
| 15 | 1710035712000 |
| 16 | 27360571392000 |
| 17 | 397533007872000 |
| 18 | 7155594141696000 |
| 19 | 147254595231744000 |
| 20 | 2945091904634880000 |
[1,3,10,40,168,1008,7920,63360,570240,5080320, 47174400,566092800,8143027200,114002380800, 1710035712000,27360571392000,397533007872000, 7155594141696000,147254595231744000, 2945091904634880000] |