The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 8 |
| 6 | 43 |
| 7 | 267 |
| 8 | 1927 |
| 9 | 15845 |
| 10 | 146123 |
| 11 | 1493701 |
| 12 | 16762640 |
| 13 | 204876709 |
| 14 | 2708925368 |
| 15 | 38526938568 |
| 16 | 586465620430 |
| 17 | 9513775620310 |
| 18 | 163848357905336 |
| 19 | 2985681188497227 |
| 20 | 57391427290002261 |
| 21 | 1160582196308934615 |
[1,0,0,1,2,8,43,267,1927,15845,146123,1493701, 16762640,204876709,2708925368,38526938568, 586465620430,9513775620310,163848357905336, 2985681188497227,57391427290002261, 1160582196308934615] |