| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 3 |
| 2 | 30 |
| 3 | 252 |
| 4 | 2040 |
| 5 | 16368 |
| 6 | 131040 |
| 7 | 1048512 |
| 8 | 8388480 |
| 9 | 67108608 |
| 10 | 536870400 |
| 11 | 4294966272 |
| 12 | 34359736320 |
| 13 | 274877902848 |
| 14 | 2199023247360 |
| 15 | 17592186028032 |
| 16 | 140737488322560 |
| 17 | 1125899906777088 |
| 18 | 9007199254609920 |
| 19 | 72057594037665792 |
[0,3,30,252,2040,16368,131040,1048512,8388480, 67108608,536870400,4294966272,34359736320, 274877902848,2199023247360,17592186028032, 140737488322560,1125899906777088,9007199254609920, 72057594037665792] |