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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 6 |
| 5 | 18 |
| 6 | 78 |
| 7 | 438 |
| 8 | 2958 |
| 9 | 23118 |
| 10 | 204558 |
| 11 | 2018958 |
| 12 | 21977358 |
| 13 | 261478158 |
| 14 | 3374988558 |
| 15 | 46964134158 |
| 16 | 700801318158 |
| 17 | 11162196262158 |
| 18 | 189005910310158 |
| 19 | 3390192763174158 |
| 20 | 64212742967590158 |
| 21 | 1280663747055910158 |
[1,2,3,6,18,78,438,2958,23118,204558,2018958, 21977358,261478158,3374988558,46964134158, 700801318158,11162196262158,189005910310158, 3390192763174158,64212742967590158, 1280663747055910158] |