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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 7 |
| 3 | 21 |
| 4 | 80 |
| 5 | 281 |
| 6 | 1132 |
| 7 | 4357 |
| 8 | 18055 |
| 9 | 73253 |
| 10 | 309022 |
| 11 | 1297469 |
| 12 | 5558459 |
| 13 | 23884194 |
| 14 | 103688068 |
| 15 | 452547704 |
| 16 | 1986992167 |
| 17 | 8770142760 |
| 18 | 38880409859 |
| 19 | 173106495312 |
| 20 | 773616763147 |
| 21 | 3468775072427 |
| 22 | 15604701398600 |
| 23 | 70387147304169 |
| 24 | 318386328824149 |
| 25 | 1443488785369466 |
| 26 | 6559809531221861 |
| 27 | 29871912150451515 |
[1,2,7,21,80,281,1132,4357,18055,73253,309022, 1297469,5558459,23884194,103688068,452547704, 1986992167,8770142760,38880409859,173106495312, 773616763147,3468775072427,15604701398600, 70387147304169,318386328824149,1443488785369466, 6559809531221861,29871912150451515] |