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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 0 |
| 3 | 7 |
| 4 | 8 |
| 5 | 51 |
| 6 | 100 |
| 7 | 407 |
| 8 | 1008 |
| 9 | 3451 |
| 10 | 9500 |
| 11 | 30207 |
| 12 | 87208 |
| 13 | 268451 |
| 14 | 791700 |
| 15 | 2402407 |
| 16 | 7152608 |
| 17 | 21567051 |
| 18 | 64482700 |
| 19 | 193885007 |
| 20 | 580781208 |
| 21 | 1744091251 |
| 22 | 5228778500 |
| 23 | 15693326007 |
| 24 | 47065997008 |
| 25 | 141225953051 |
| 26 | 423621935100 |
| 27 | 1270977653407 |
[0,1,0,7,8,51,100,407,1008,3451,9500,30207,87208, 268451,791700,2402407,7152608,21567051,64482700, 193885007,580781208,1744091251,5228778500, 15693326007,47065997008,141225953051,423621935100, 1270977653407] |