| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 18 |
| 3 | 224 |
| 4 | 3230 |
| 5 | 50688 |
| 6 | 840420 |
| 7 | 14483456 |
| 8 | 256856886 |
| 9 | 4656988160 |
| 10 | 85929839996 |
| 11 | 1608379269120 |
| 12 | 30463651429484 |
| 13 | 582796191989760 |
| 14 | 11245047027447240 |
| 15 | 218581150665277440 |
| 16 | 4276257634911525670 |
| 17 | 84135742205488791552 |
| 18 | 1663738200769421021580 |
| 19 | 33047906167191995678720 |
[1,2,18,224,3230,50688,840420,14483456,256856886, 4656988160,85929839996,1608379269120, 30463651429484,582796191989760,11245047027447240, 218581150665277440,4276257634911525670, 84135742205488791552,1663738200769421021580, 33047906167191995678720] |