The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 16 |
| 5 | 124 |
| 6 | 1256 |
| 7 | 15576 |
| 8 | 226248 |
| 9 | 3729216 |
| 10 | 68179968 |
| 11 | 1361836800 |
| 12 | 29501349120 |
| 13 | 693638208000 |
| 14 | 17815908096000 |
| 15 | 502048890201600 |
| 16 | 15388268595840000 |
| 17 | 500579319427891200 |
| 18 | 16817771937344716800 |
| 19 | 581609175119297740800 |
[1,1,3,16,124,1256,15576,226248,3729216,68179968, 1361836800,29501349120,693638208000, 17815908096000,502048890201600,15388268595840000, 500579319427891200,16817771937344716800, 581609175119297740800] |