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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 1 |
| 7 | 2 |
| 8 | 7 |
| 9 | 16 |
| 10 | 37 |
| 11 | 76 |
| 12 | 166 |
| 13 | 328 |
| 14 | 669 |
| 15 | 1326 |
| 16 | 2626 |
| 17 | 5138 |
| 18 | 10104 |
| 19 | 19680 |
| 20 | 38442 |
| 21 | 74822 |
| 22 | 145715 |
| 23 | 283424 |
| 24 | 551721 |
| 25 | 1073224 |
[0,0,0,0,0,1,2,7,16,37,76,166,328,669,1326,2626, 5138,10104,19680,38442,74822,145715,283424,551721, 1073224] |