The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 12 |
| 5 | 140 |
| 6 | 1470 |
| 7 | 10122 |
| 8 | 114296 |
| 9 | 1874952 |
| 10 | 25462170 |
| 11 | 379431470 |
| 12 | 7546461252 |
| 13 | 151797222876 |
| 14 | 3066316693622 |
| 15 | 72101615826450 |
| 16 | 1843378516587120 |
| 17 | 47860832586054032 |
| 18 | 1338908395558366386 |
| 19 | 40675047500003794902 |
| 20 | 1282380661224172506620 |
[1,0,2,6,12,140,1470,10122,114296,1874952, 25462170,379431470,7546461252,151797222876, 3066316693622,72101615826450,1843378516587120, 47860832586054032,1338908395558366386, 40675047500003794902,1282380661224172506620] |