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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 19 |
| 5 | 54 |
| 6 | 180 |
| 7 | 508 |
| 8 | 1533 |
| 9 | 4332 |
| 10 | 13041 |
| 11 | 37492 |
| 12 | 111367 |
| 13 | 326636 |
| 14 | 968802 |
| 15 | 2858460 |
| 16 | 8483290 |
| 17 | 25113618 |
| 18 | 74512947 |
| 19 | 220885446 |
| 20 | 655274837 |
| 21 | 1943117294 |
| 22 | 5763235194 |
| 23 | 17089323366 |
| 24 | 50673594159 |
| 25 | 150232437482 |
| 26 | 445359235627 |
| 27 | 1320070201468 |
[0,1,4,19,54,180,508,1533,4332,13041,37492,111367, 326636,968802,2858460,8483290,25113618,74512947, 220885446,655274837,1943117294,5763235194, 17089323366,50673594159,150232437482,445359235627, 1320070201468] |