| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 38 |
| 3 | 328 |
| 4 | 2686 |
| 5 | 21224 |
| 6 | 163982 |
| 7 | 1249784 |
| 8 | 9447102 |
| 9 | 71056840 |
| 10 | 532854638 |
| 11 | 3988597144 |
| 12 | 29822927134 |
| 13 | 222836912744 |
| 14 | 1664351910350 |
| 15 | 12427793513528 |
| 16 | 92784673372542 |
| 17 | 692656225953544 |
| 18 | 5170521713987630 |
| 19 | 38595421782328024 |
| 20 | 288089831076277726 |
| 21 | 2150375933904641960 |
[0,4,38,328,2686,21224,163982,1249784,9447102, 71056840,532854638,3988597144,29822927134, 222836912744,1664351910350,12427793513528, 92784673372542,692656225953544,5170521713987630, 38595421782328024,288089831076277726, 2150375933904641960] |