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| n | a(n) |
|---|---|
| 1 | 6 |
| 2 | 90 |
| 3 | 810 |
| 4 | 5508 |
| 5 | 31590 |
| 6 | 161838 |
| 7 | 765450 |
| 8 | 3411720 |
| 9 | 14526054 |
| 10 | 59639490 |
| 11 | 237731274 |
| 12 | 924707340 |
| 13 | 3523453830 |
| 14 | 13191428502 |
| 15 | 48642794730 |
| 16 | 177008116752 |
| 17 | 636661003590 |
| 18 | 2266409860650 |
| 19 | 7994034370026 |
| 20 | 27964010896020 |
| 21 | 97092998430246 |
[6,90,810,5508,31590,161838,765450,3411720, 14526054,59639490,237731274,924707340,3523453830, 13191428502,48642794730,177008116752,636661003590, 2266409860650,7994034370026,27964010896020, 97092998430246] |