The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 180 |
| 3 | 1320 |
| 4 | 7920 |
| 5 | 41184 |
| 6 | 192192 |
| 7 | 823680 |
| 8 | 3294720 |
| 9 | 12446720 |
| 10 | 44808192 |
| 11 | 154791936 |
| 12 | 515973120 |
| 13 | 1666990080 |
| 14 | 5239111680 |
| 15 | 16066609152 |
| 16 | 48199827456 |
| 17 | 141764198400 |
| 18 | 409541017600 |
| 19 | 1163958681600 |
| 20 | 3259084308480 |
| 21 | 9001280471040 |
[1,18,180,1320,7920,41184,192192,823680,3294720, 12446720,44808192,154791936,515973120,1666990080, 5239111680,16066609152,48199827456,141764198400, 409541017600,1163958681600,3259084308480, 9001280471040] |