The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 36 |
| 5 | 420 |
| 6 | 6120 |
| 7 | 94920 |
| 8 | 1599360 |
| 9 | 30844800 |
| 10 | 694008000 |
| 11 | 17786260800 |
| 12 | 502352928000 |
| 13 | 15367975983360 |
| 14 | 507522467612160 |
| 15 | 18092546664192000 |
| 16 | 694083913915392000 |
| 17 | 28487571264011059200 |
| 18 | 1243715592543834009600 |
| 19 | 57518280664660995379200 |
| 20 | 2809850302506602234880000 |
[1,1,2,6,36,420,6120,94920,1599360,30844800, 694008000,17786260800,502352928000,15367975983360, 507522467612160,18092546664192000, 694083913915392000,28487571264011059200, 1243715592543834009600,57518280664660995379200, 2809850302506602234880000] |