The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 12 |
| 4 | 40 |
| 5 | 120 |
| 6 | 288 |
| 7 | 1092 |
| 8 | 3072 |
| 9 | 7776 |
| 10 | 23600 |
| 11 | 87120 |
| 12 | 259200 |
| 13 | 797160 |
| 14 | 1847104 |
| 15 | 5832000 |
| 16 | 21523360 |
| 17 | 63672480 |
| 18 | 152845056 |
| 19 | 580921200 |
| 20 | 1700870400 |
| 21 | 4368821184 |
| 22 | 12550120000 |
| 23 | 47071589412 |
| 24 | 130459631616 |
| 25 | 413939700000 |
| 26 | 997562438080 |
| 27 | 3012122557440 |
| 28 | 11159367815680 |
[1,2,4,12,40,120,288,1092,3072,7776,23600,87120, 259200,797160,1847104,5832000,21523360,63672480, 152845056,580921200,1700870400,4368821184, 12550120000,47071589412,130459631616,413939700000, 997562438080,3012122557440,11159367815680] |