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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 3 |
| 6 | 6 |
| 7 | 15 |
| 8 | 28 |
| 9 | 58 |
| 10 | 132 |
| 11 | 254 |
| 12 | 515 |
| 13 | 1042 |
| 14 | 2088 |
| 15 | 4172 |
| 16 | 8337 |
| 17 | 16720 |
| 18 | 33556 |
| 19 | 66948 |
| 20 | 134088 |
| 21 | 268037 |
| 22 | 535435 |
| 23 | 1069932 |
| 24 | 2139357 |
| 25 | 4275948 |
| 26 | 8544351 |
| 27 | 17076036 |
[0,0,0,0,2,3,6,15,28,58,132,254,515,1042,2088, 4172,8337,16720,33556,66948,134088,268037,535435, 1069932,2139357,4275948,8544351,17076036] |