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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 31 |
| 3 | 298 |
| 4 | 3199 |
| 5 | 36742 |
| 6 | 441748 |
| 7 | 5489554 |
| 8 | 69945295 |
| 9 | 908836768 |
| 10 | 11996580199 |
| 11 | 160418984656 |
| 12 | 2168512922692 |
| 13 | 29584600414168 |
| 14 | 406823494817560 |
| 15 | 5632906243123090 |
| 16 | 78465351036084655 |
| 17 | 1098851032467132484 |
| 18 | 15461857967408794333 |
| 19 | 218490450548650811914 |
[1,4,31,298,3199,36742,441748,5489554,69945295, 908836768,11996580199,160418984656,2168512922692, 29584600414168,406823494817560,5632906243123090, 78465351036084655,1098851032467132484, 15461857967408794333,218490450548650811914] |