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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 8 |
| 4 | 60 |
| 5 | 296 |
| 6 | 1126 |
| 7 | 4237 |
| 8 | 24210 |
| 9 | 91541 |
| 10 | 440533 |
| 11 | 1942297 |
| 12 | 8497706 |
| 13 | 37987962 |
| 14 | 169158221 |
| 15 | 750990638 |
| 16 | 3344857959 |
| 17 | 14827515754 |
| 18 | 65958541835 |
| 19 | 293291341441 |
| 20 | 1303464660150 |
| 21 | 5793684155190 |
| 22 | 25748199147004 |
| 23 | 114445600714047 |
[0,2,8,60,296,1126,4237,24210,91541,440533, 1942297,8497706,37987962,169158221,750990638, 3344857959,14827515754,65958541835,293291341441, 1303464660150,5793684155190,25748199147004, 114445600714047] |