| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 52 |
| 3 | 408 |
| 4 | 3280 |
| 5 | 26208 |
| 6 | 209728 |
| 7 | 1677696 |
| 8 | 13421824 |
| 9 | 107374080 |
| 10 | 858993664 |
| 11 | 6871947264 |
| 12 | 54975582208 |
| 13 | 439804649472 |
| 14 | 3518437212160 |
| 15 | 28147497664512 |
| 16 | 225179981381632 |
| 17 | 1801439850921984 |
| 18 | 14411518807638016 |
| 19 | 115292150460579840 |
[1,6,52,408,3280,26208,209728,1677696,13421824, 107374080,858993664,6871947264,54975582208, 439804649472,3518437212160,28147497664512, 225179981381632,1801439850921984, 14411518807638016,115292150460579840] |