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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 3 |
| 2 | 10 |
| 3 | 35 |
| 4 | 100 |
| 5 | 288 |
| 6 | 780 |
| 7 | 2115 |
| 8 | 5610 |
| 9 | 14883 |
| 10 | 39160 |
| 11 | 103040 |
| 12 | 270280 |
| 13 | 708963 |
| 14 | 1857450 |
| 15 | 4866435 |
| 16 | 12744060 |
| 17 | 33373728 |
| 18 | 87382900 |
| 19 | 228795875 |
| 20 | 599019850 |
| 21 | 1568318403 |
| 22 | 4105974960 |
| 23 | 10749749760 |
| 24 | 28143378000 |
| 25 | 73680759363 |
| 26 | 192899171530 |
| 27 | 505017737315 |
| 28 | 1322154751060 |
[0,3,10,35,100,288,780,2115,5610,14883,39160, 103040,270280,708963,1857450,4866435,12744060, 33373728,87382900,228795875,599019850,1568318403, 4105974960,10749749760,28143378000,73680759363, 192899171530,505017737315,1322154751060] |