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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 3 |
| 4 | 15 |
| 5 | 45 |
| 6 | 147 |
| 7 | 402 |
| 8 | 1134 |
| 9 | 2991 |
| 10 | 7917 |
| 11 | 20367 |
| 12 | 52167 |
| 13 | 131748 |
| 14 | 330876 |
| 15 | 824187 |
| 16 | 2042763 |
| 17 | 5035473 |
| 18 | 12361755 |
| 19 | 30226614 |
| 20 | 73664298 |
| 21 | 178971879 |
| 22 | 433649769 |
| 23 | 1048133619 |
| 24 | 2527706127 |
| 25 | 6083434824 |
| 26 | 14613750648 |
| 27 | 35045236083 |
| 28 | 83909261319 |
[0,0,0,3,15,45,147,402,1134,2991,7917,20367,52167, 131748,330876,824187,2042763,5035473,12361755, 30226614,73664298,178971879,433649769,1048133619, 2527706127,6083434824,14613750648,35045236083, 83909261319] |