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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 15 |
| 6 | 51 |
| 7 | 175 |
| 8 | 573 |
| 9 | 1866 |
| 10 | 5978 |
| 11 | 19000 |
| 12 | 59859 |
| 13 | 187503 |
| 14 | 584012 |
| 15 | 1811212 |
| 16 | 5595239 |
| 17 | 17228943 |
| 18 | 52898764 |
| 19 | 162013452 |
| 20 | 495100454 |
| 21 | 1510029296 |
| 22 | 4597430832 |
| 23 | 13975327501 |
| 24 | 42422033217 |
| 25 | 128606150706 |
| 26 | 389423872694 |
| 27 | 1177925775148 |
| 28 | 3559477190797 |
| 29 | 10746362772325 |
[0,0,1,4,15,51,175,573,1866,5978,19000,59859, 187503,584012,1811212,5595239,17228943,52898764, 162013452,495100454,1510029296,4597430832, 13975327501,42422033217,128606150706,389423872694, 1177925775148,3559477190797,10746362772325] |