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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 124 |
| 4 | 631 |
| 5 | 2780 |
| 6 | 12954 |
| 7 | 55196 |
| 8 | 241634 |
| 9 | 1012196 |
| 10 | 4280046 |
| 11 | 17636252 |
| 12 | 73157709 |
| 13 | 298342936 |
| 14 | 1220952044 |
| 15 | 4947485904 |
| 16 | 20079338277 |
| 17 | 80987461760 |
| 18 | 326986050564 |
| 19 | 1314939934216 |
| 20 | 5290893771329 |
| 21 | 21236552526364 |
| 22 | 85263892578686 |
| 23 | 341801704446572 |
| 24 | 1370448001291679 |
[1,4,26,124,631,2780,12954,55196,241634,1012196, 4280046,17636252,73157709,298342936,1220952044, 4947485904,20079338277,80987461760,326986050564, 1314939934216,5290893771329,21236552526364, 85263892578686,341801704446572,1370448001291679] |