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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 73 |
| 5 | 282 |
| 6 | 1138 |
| 7 | 4740 |
| 8 | 20238 |
| 9 | 88143 |
| 10 | 390061 |
| 11 | 1749068 |
| 12 | 7929891 |
| 13 | 36288683 |
| 14 | 167390945 |
| 15 | 777445430 |
| 16 | 3632416696 |
| 17 | 17060267774 |
| 18 | 80495119152 |
| 19 | 381346095317 |
| 20 | 1813181750079 |
| 21 | 8649079106026 |
| 22 | 41377306954577 |
| 23 | 198469912424497 |
| 24 | 954244174488097 |
| 25 | 4597930637100167 |
| 26 | 22198334919108379 |
| 27 | 107364372879141877 |
[1,2,6,20,73,282,1138,4740,20238,88143,390061, 1749068,7929891,36288683,167390945,777445430, 3632416696,17060267774,80495119152,381346095317, 1813181750079,8649079106026,41377306954577, 198469912424497,954244174488097,4597930637100167, 22198334919108379,107364372879141877] |