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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 15 |
| 4 | 57 |
| 5 | 218 |
| 6 | 837 |
| 7 | 3224 |
| 8 | 12455 |
| 9 | 48244 |
| 10 | 187307 |
| 11 | 728692 |
| 12 | 2839877 |
| 13 | 11084756 |
| 14 | 43325744 |
| 15 | 169548783 |
| 16 | 664229072 |
| 17 | 2604770882 |
| 18 | 10223744018 |
| 19 | 40161025704 |
| 20 | 157878855072 |
| 21 | 621070768564 |
| 22 | 2444741008686 |
| 23 | 9628942865104 |
| 24 | 37945470536353 |
| 25 | 149609922922904 |
| 26 | 590153796979867 |
[0,1,4,15,57,218,837,3224,12455,48244,187307, 728692,2839877,11084756,43325744,169548783, 664229072,2604770882,10223744018,40161025704, 157878855072,621070768564,2444741008686, 9628942865104,37945470536353,149609922922904, 590153796979867] |