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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 81 |
| 6 | 561 |
| 7 | 4683 |
| 8 | 44415 |
| 9 | 479241 |
| 10 | 5793921 |
| 11 | 77332563 |
| 12 | 1130944815 |
| 13 | 17984844801 |
| 14 | 308888337681 |
| 15 | 5698762943643 |
| 16 | 112401325405215 |
| 17 | 2360158641832761 |
| 18 | 52564270139375841 |
| 19 | 1237645528139173923 |
| 20 | 30717272450961249615 |
| 21 | 801500394828539219121 |
[1,1,3,15,81,561,4683,44415,479241,5793921, 77332563,1130944815,17984844801,308888337681, 5698762943643,112401325405215,2360158641832761, 52564270139375841,1237645528139173923, 30717272450961249615,801500394828539219121] |