The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 21 |
| 2 | 252 |
| 3 | 2268 |
| 4 | 17052 |
| 5 | 115290 |
| 6 | 741636 |
| 7 | 4705452 |
| 8 | 29807631 |
| 9 | 187564167 |
| 10 | 1160653536 |
| 11 | 7015318632 |
| 12 | 41344513938 |
| 13 | 237976030404 |
| 14 | 1341887545224 |
| 15 | 7435262750328 |
| 16 | 40583278223901 |
| 17 | 218600645068953 |
| 18 | 1163518783578900 |
| 19 | 6125571713285892 |
| 20 | 31925464081249032 |
| 21 | 164844714547081134 |
[1,21,252,2268,17052,115290,741636,4705452, 29807631,187564167,1160653536,7015318632, 41344513938,237976030404,1341887545224, 7435262750328,40583278223901,218600645068953, 1163518783578900,6125571713285892, 31925464081249032,164844714547081134] |