| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 75 |
| 5 | 366 |
| 6 | 1887 |
| 7 | 10010 |
| 8 | 54493 |
| 9 | 302302 |
| 10 | 1703599 |
| 11 | 9723774 |
| 12 | 56101292 |
| 13 | 326640411 |
| 14 | 1916800425 |
| 15 | 11325242328 |
| 16 | 67316128903 |
| 17 | 402245682741 |
| 18 | 2414978550718 |
| 19 | 14560379165160 |
| 20 | 88122911824659 |
| 21 | 535188028077586 |
| 22 | 3260549998701951 |
| 23 | 19921639754064470 |
| 24 | 122041156818328779 |
[1,1,4,16,75,366,1887,10010,54493,302302,1703599, 9723774,56101292,326640411,1916800425,11325242328, 67316128903,402245682741,2414978550718, 14560379165160,88122911824659,535188028077586, 3260549998701951,19921639754064470, 122041156818328779] |