The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 28 |
| 5 | 281 |
| 6 | 3658 |
| 7 | 58257 |
| 8 | 1093228 |
| 9 | 23558599 |
| 10 | 572266776 |
| 11 | 15452506280 |
| 12 | 458821151228 |
| 13 | 14851492994252 |
| 14 | 520354780202214 |
| 15 | 19618194420629803 |
| 16 | 791884055353155776 |
| 17 | 34073795479759377099 |
| 18 | 1556996042454725399980 |
| 19 | 75302117386217875215016 |
| 20 | 3843109109512227994295960 |
| 21 | 206418937612873398754242802 |
[1,1,4,28,281,3658,58257,1093228,23558599, 572266776,15452506280,458821151228,14851492994252, 520354780202214,19618194420629803, 791884055353155776,34073795479759377099, 1556996042454725399980,75302117386217875215016, 3843109109512227994295960, 206418937612873398754242802] |