| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 20 |
| 3 | 220 |
| 4 | 2280 |
| 5 | 25920 |
| 6 | 443744 |
| 7 | 10057408 |
| 8 | 215047552 |
| 9 | 3841564160 |
| 10 | 57161584256 |
| 11 | 757459114112 |
| 12 | 10427052678656 |
| 13 | 166827795710208 |
| 14 | 2728593278189568 |
| 15 | 38108069305433088 |
| 16 | 521570277192555520 |
| 17 | 14195894062729323520 |
| 18 | 594582326909611536384 |
| 19 | 21399757674339677249536 |
[1,2,20,220,2280,25920,443744,10057408,215047552, 3841564160,57161584256,757459114112, 10427052678656,166827795710208,2728593278189568, 38108069305433088,521570277192555520, 14195894062729323520,594582326909611536384, 21399757674339677249536] |