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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 11 |
| 5 | 23 |
| 6 | 72 |
| 7 | 201 |
| 8 | 597 |
| 9 | 1705 |
| 10 | 5141 |
| 11 | 15305 |
| 12 | 45558 |
| 13 | 136366 |
| 14 | 408269 |
| 15 | 1222895 |
| 16 | 3664732 |
| 17 | 10990002 |
| 18 | 32961810 |
| 19 | 98879571 |
| 20 | 296674303 |
| 21 | 890217834 |
| 22 | 2671430941 |
| 23 | 8017066909 |
| 24 | 24060553805 |
| 25 | 72211714389 |
| 26 | 216729874503 |
| 27 | 650484059608 |
[0,2,4,11,23,72,201,597,1705,5141,15305,45558, 136366,408269,1222895,3664732,10990002,32961810, 98879571,296674303,890217834,2671430941, 8017066909,24060553805,72211714389,216729874503, 650484059608] |