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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 32 |
| 3 | 292 |
| 4 | 2816 |
| 5 | 28004 |
| 6 | 284000 |
| 7 | 2919620 |
| 8 | 30316544 |
| 9 | 317222212 |
| 10 | 3339504032 |
| 11 | 35329425124 |
| 12 | 375282559232 |
| 13 | 4000059761572 |
| 14 | 42760427177696 |
| 15 | 458259268924292 |
| 16 | 4921911787962368 |
| 17 | 52965710906750084 |
| 18 | 570951048018417440 |
| 19 | 6164049197776406180 |
| 20 | 66639047280436354816 |
[1,4,32,292,2816,28004,284000,2919620,30316544, 317222212,3339504032,35329425124,375282559232, 4000059761572,42760427177696,458259268924292, 4921911787962368,52965710906750084, 570951048018417440,6164049197776406180, 66639047280436354816] |