| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 4 |
| 6 | 14 |
| 7 | 54 |
| 8 | 332 |
| 9 | 2246 |
| 10 | 18264 |
| 11 | 164950 |
| 12 | 1664354 |
| 13 | 18423144 |
| 14 | 222406776 |
| 15 | 2905943328 |
| 16 | 40865005494 |
| 17 | 615376173184 |
| 18 | 9880209206458 |
| 19 | 168483518571798 |
| 20 | 3041127561315224 |
| 21 | 57926238289970076 |
| 22 | 1161157777643184900 |
| 23 | 24434798429947993054 |
| 24 | 538583682082245127336 |
[1,1,1,2,4,14,54,332,2246,18264,164950,1664354, 18423144,222406776,2905943328,40865005494, 615376173184,9880209206458,168483518571798, 3041127561315224,57926238289970076, 1161157777643184900,24434798429947993054, 538583682082245127336] |