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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 6 |
| 3 | 25 |
| 4 | 90 |
| 5 | 306 |
| 6 | 1004 |
| 7 | 3226 |
| 8 | 10218 |
| 9 | 32043 |
| 10 | 99748 |
| 11 | 308787 |
| 12 | 951772 |
| 13 | 2923563 |
| 14 | 8955342 |
| 15 | 27368895 |
| 16 | 83484042 |
| 17 | 254244033 |
| 18 | 773219196 |
| 19 | 2348780937 |
| 20 | 7127522136 |
| 21 | 21609615822 |
| 22 | 65465845254 |
| 23 | 198189732798 |
| 24 | 599624708588 |
| 25 | 1813169256151 |
| 26 | 5480019176754 |
| 27 | 16555101318735 |
[0,1,6,25,90,306,1004,3226,10218,32043,99748, 308787,951772,2923563,8955342,27368895,83484042, 254244033,773219196,2348780937,7127522136, 21609615822,65465845254,198189732798,599624708588, 1813169256151,5480019176754,16555101318735] |