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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 42 |
| 5 | 144 |
| 6 | 558 |
| 7 | 2115 |
| 8 | 8365 |
| 9 | 32835 |
| 10 | 134882 |
| 11 | 549528 |
| 12 | 2286600 |
| 13 | 9483263 |
| 14 | 40231902 |
| 15 | 170084068 |
| 16 | 727936899 |
| 17 | 3111265619 |
| 18 | 13473412479 |
| 19 | 58262030565 |
| 20 | 253926141635 |
| 21 | 1106269232727 |
| 22 | 4859865964520 |
| 23 | 21339504293971 |
| 24 | 94204444105176 |
| 25 | 415914724112337 |
| 26 | 1846601894388353 |
| 27 | 8198945952462282 |
[1,1,4,12,42,144,558,2115,8365,32835,134882, 549528,2286600,9483263,40231902,170084068, 727936899,3111265619,13473412479,58262030565, 253926141635,1106269232727,4859865964520, 21339504293971,94204444105176,415914724112337, 1846601894388353,8198945952462282] |