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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 9 |
| 5 | 22 |
| 6 | 57 |
| 7 | 156 |
| 8 | 447 |
| 9 | 1332 |
| 10 | 4103 |
| 11 | 12999 |
| 12 | 42176 |
| 13 | 139638 |
| 14 | 470353 |
| 15 | 1607861 |
| 16 | 5566543 |
| 17 | 19484810 |
| 18 | 68859862 |
| 19 | 245404650 |
| 20 | 881081082 |
| 21 | 3184214751 |
| 22 | 11575346316 |
| 23 | 42300703150 |
| 24 | 155316289004 |
| 25 | 572725968326 |
| 26 | 2120154235114 |
| 27 | 7876449597257 |
| 28 | 29356608044002 |
[1,1,2,4,9,22,57,156,447,1332,4103,12999,42176, 139638,470353,1607861,5566543,19484810,68859862, 245404650,881081082,3184214751,11575346316, 42300703150,155316289004,572725968326, 2120154235114,7876449597257,29356608044002] |