The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | -1 |
| 1 | -1 |
| 2 | 1 |
| 3 | -2 |
| 4 | 6 |
| 5 | -24 |
| 6 | 120 |
| 7 | -720 |
| 8 | 5040 |
| 9 | -40320 |
| 10 | 362880 |
| 11 | -3628800 |
| 12 | 39916800 |
| 13 | -479001600 |
| 14 | 6227020800 |
| 15 | -87178291200 |
| 16 | 1307674368000 |
| 17 | -20922789888000 |
| 18 | 355687428096000 |
| 19 | -6402373705728000 |
| 20 | 121645100408832000 |
[-1,-1,1,-2,6,-24,120,-720,5040,-40320,362880, -3628800,39916800,-479001600,6227020800, -87178291200,1307674368000,-20922789888000, 355687428096000,-6402373705728000, 121645100408832000] |