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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 20 |
| 5 | 73 |
| 6 | 281 |
| 7 | 1125 |
| 8 | 4635 |
| 9 | 19525 |
| 10 | 83710 |
| 11 | 364070 |
| 12 | 1602327 |
| 13 | 7123041 |
| 14 | 31937010 |
| 15 | 144255802 |
| 16 | 655804649 |
| 17 | 2998354717 |
| 18 | 13777825186 |
| 19 | 63596593430 |
| 20 | 294743653360 |
| 21 | 1371017707245 |
| 22 | 6398580086645 |
| 23 | 29952930770185 |
| 24 | 140604572777250 |
| 25 | 661708404611603 |
| 26 | 3121439743413256 |
| 27 | 14756658303857332 |
[1,2,6,20,73,281,1125,4635,19525,83710,364070, 1602327,7123041,31937010,144255802,655804649, 2998354717,13777825186,63596593430,294743653360, 1371017707245,6398580086645,29952930770185, 140604572777250,661708404611603,3121439743413256, 14756658303857332] |