The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 54 |
| 3 | 648 |
| 4 | 7500 |
| 5 | 85440 |
| 6 | 965202 |
| 7 | 10849552 |
| 8 | 121566744 |
| 9 | 1359160020 |
| 10 | 15172321890 |
| 11 | 169175039616 |
| 12 | 1884704860116 |
| 13 | 20982512553912 |
| 14 | 233474575117770 |
| 15 | 2596777575029280 |
| 16 | 28872014164369968 |
| 17 | 320917108809011868 |
| 18 | 3566175414049854306 |
| 19 | 39620770883613043240 |
| 20 | 440115513924937822020 |
[0,4,54,648,7500,85440,965202,10849552,121566744, 1359160020,15172321890,169175039616,1884704860116, 20982512553912,233474575117770,2596777575029280, 28872014164369968,320917108809011868, 3566175414049854306,39620770883613043240, 440115513924937822020] |