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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 121 |
| 4 | 873 |
| 5 | 6606 |
| 6 | 51728 |
| 7 | 415629 |
| 8 | 3407391 |
| 9 | 28388847 |
| 10 | 239675406 |
| 11 | 2045980440 |
| 12 | 17629939980 |
| 13 | 153142537440 |
| 14 | 1339599358944 |
| 15 | 11789960853293 |
| 16 | 104327344928619 |
| 17 | 927627432162129 |
| 18 | 8283625668834238 |
| 19 | 74259685465582569 |
| 20 | 668054892245119353 |
[1,3,18,121,873,6606,51728,415629,3407391, 28388847,239675406,2045980440,17629939980, 153142537440,1339599358944,11789960853293, 104327344928619,927627432162129,8283625668834238, 74259685465582569,668054892245119353] |