| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 18 |
| 3 | 86 |
| 4 | 422 |
| 5 | 2094 |
| 6 | 10438 |
| 7 | 52126 |
| 8 | 260502 |
| 9 | 1302254 |
| 10 | 6510758 |
| 11 | 32552766 |
| 12 | 162761782 |
| 13 | 813804814 |
| 14 | 4069015878 |
| 15 | 20345063006 |
| 16 | 101725282262 |
| 17 | 508626345774 |
| 18 | 2543131597798 |
| 19 | 12715657726846 |
| 20 | 63578288109942 |
| 21 | 317891439501134 |
[1,4,18,86,422,2094,10438,52126,260502,1302254, 6510758,32552766,162761782,813804814,4069015878, 20345063006,101725282262,508626345774, 2543131597798,12715657726846,63578288109942, 317891439501134] |