| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 13 |
| 4 | 71 |
| 5 | 463 |
| 6 | 3497 |
| 7 | 29975 |
| 8 | 287265 |
| 9 | 3042545 |
| 10 | 35284315 |
| 11 | 444617525 |
| 12 | 6048575335 |
| 13 | 88347242335 |
| 14 | 1378930649745 |
| 15 | 22903345844335 |
| 16 | 403342641729665 |
| 17 | 7506843094993825 |
| 18 | 147226845692229875 |
| 19 | 3034786640911840925 |
| 20 | 65592491119118514375 |
[1,1,3,13,71,463,3497,29975,287265,3042545, 35284315,444617525,6048575335,88347242335, 1378930649745,22903345844335,403342641729665, 7506843094993825,147226845692229875, 3034786640911840925,65592491119118514375] |