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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 13 |
| 5 | 31 |
| 6 | 91 |
| 7 | 313 |
| 8 | 988 |
| 9 | 3095 |
| 10 | 10377 |
| 11 | 35146 |
| 12 | 117682 |
| 13 | 400117 |
| 14 | 1381582 |
| 15 | 4779997 |
| 16 | 16599766 |
| 17 | 58095076 |
| 18 | 204319835 |
| 19 | 720756820 |
| 20 | 2552544940 |
| 21 | 9074710255 |
| 22 | 32356325145 |
| 23 | 115679362789 |
| 24 | 414701335849 |
| 25 | 1490297002000 |
| 26 | 5367227015647 |
| 27 | 19369656905210 |
| 28 | 70038419041844 |
[1,1,1,4,13,31,91,313,988,3095,10377,35146,117682, 400117,1381582,4779997,16599766,58095076, 204319835,720756820,2552544940,9074710255, 32356325145,115679362789,414701335849, 1490297002000,5367227015647,19369656905210, 70038419041844] |