The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 8 |
| 5 | 44 |
| 6 | 264 |
| 7 | 1854 |
| 8 | 14832 |
| 9 | 133496 |
| 10 | 1334960 |
| 11 | 14684570 |
| 12 | 176214840 |
| 13 | 2290792932 |
| 14 | 32071101048 |
| 15 | 481066515734 |
| 16 | 7697064251744 |
| 17 | 130850092279664 |
| 18 | 2355301661033952 |
| 19 | 44750731559645106 |
| 20 | 895014631192902120 |
[0,0,2,8,44,264,1854,14832,133496,1334960, 14684570,176214840,2290792932,32071101048, 481066515734,7697064251744,130850092279664, 2355301661033952,44750731559645106, 895014631192902120] |