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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 7 |
| 3 | 55 |
| 4 | 505 |
| 5 | 5497 |
| 6 | 69823 |
| 7 | 1007407 |
| 8 | 16157905 |
| 9 | 284214097 |
| 10 | 5432922775 |
| 11 | 112034017735 |
| 12 | 2476196276617 |
| 13 | 58332035387017 |
| 14 | 1457666574447247 |
| 15 | 38485034941511935 |
| 16 | 1069787864231083297 |
| 17 | 31213730550761076769 |
| 18 | 953352927192964243879 |
| 19 | 30406448846308128741847 |
[1,1,7,55,505,5497,69823,1007407,16157905, 284214097,5432922775,112034017735,2476196276617, 58332035387017,1457666574447247,38485034941511935, 1069787864231083297,31213730550761076769, 953352927192964243879,30406448846308128741847] |