The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | -2 |
| 3 | -2 |
| 4 | 6 |
| 5 | 6 |
| 6 | -20 |
| 7 | -20 |
| 8 | 70 |
| 9 | 70 |
| 10 | -252 |
| 11 | -252 |
| 12 | 924 |
| 13 | 924 |
| 14 | -3432 |
| 15 | -3432 |
| 16 | 12870 |
| 17 | 12870 |
| 18 | -48620 |
| 19 | -48620 |
| 20 | 184756 |
| 21 | 184756 |
| 22 | -705432 |
| 23 | -705432 |
| 24 | 2704156 |
| 25 | 2704156 |
| 26 | -10400600 |
| 27 | -10400600 |
| 28 | 40116600 |
| 29 | 40116600 |
| 30 | -155117520 |
| 31 | -155117520 |
[1,1,-2,-2,6,6,-20,-20,70,70,-252,-252,924,924, -3432,-3432,12870,12870,-48620,-48620,184756, 184756,-705432,-705432,2704156,2704156,-10400600, -10400600,40116600,40116600,-155117520,-155117520] |