The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 12 |
| 4 | 90 |
| 5 | 528 |
| 6 | 3372 |
| 7 | 20880 |
| 8 | 130728 |
| 9 | 815232 |
| 10 | 5091120 |
| 11 | 31777728 |
| 12 | 198386592 |
| 13 | 1238434560 |
| 14 | 7731150528 |
| 15 | 48262685952 |
| 16 | 301286851200 |
| 17 | 1880825008128 |
| 18 | 11741315949312 |
| 19 | 73296813911040 |
| 20 | 457565678934528 |
| 21 | 2856418110492672 |
| 22 | 17831591947054080 |
| 23 | 111316221335113728 |
[0,3,12,90,528,3372,20880,130728,815232,5091120, 31777728,198386592,1238434560,7731150528, 48262685952,301286851200,1880825008128, 11741315949312,73296813911040,457565678934528, 2856418110492672,17831591947054080, 111316221335113728] |