The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 224 |
| 5 | 2649 |
| 6 | 38880 |
| 7 | 679449 |
| 8 | 13749248 |
| 9 | 315919665 |
| 10 | 8122432000 |
| 11 | 231002307449 |
| 12 | 7199799644160 |
| 13 | 244028744225993 |
| 14 | 8936047251296256 |
| 15 | 351569799174274425 |
| 16 | 14789182545666244608 |
| 17 | 662389019735008588129 |
| 18 | 31470659616611382460416 |
| 19 | 1580849762199983023572313 |
[0,1,4,25,224,2649,38880,679449,13749248, 315919665,8122432000,231002307449,7199799644160, 244028744225993,8936047251296256, 351569799174274425,14789182545666244608, 662389019735008588129,31470659616611382460416, 1580849762199983023572313] |