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| n | a(n) |
|---|---|
| 1 | 18 |
| 2 | 324 |
| 3 | 1526 |
| 4 | 7165 |
| 5 | 40838 |
| 6 | 197256 |
| 7 | 886959 |
| 8 | 4132837 |
| 9 | 18825154 |
| 10 | 83118767 |
| 11 | 366894032 |
| 12 | 1612009910 |
| 13 | 7003691520 |
| 14 | 30295384994 |
| 15 | 130694823493 |
| 16 | 561304207068 |
| 17 | 2402966839572 |
| 18 | 10265912202332 |
| 19 | 43759103277417 |
| 20 | 186155560434801 |
[18,324,1526,7165,40838,197256,886959,4132837, 18825154,83118767,366894032,1612009910,7003691520, 30295384994,130694823493,561304207068, 2402966839572,10265912202332,43759103277417, 186155560434801] |