This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 5 |
| 1 | 15 |
| 2 | 45 |
| 3 | 135 |
| 4 | 405 |
| 5 | 1215 |
| 6 | 3645 |
| 7 | 10935 |
| 8 | 32805 |
| 9 | 98415 |
| 10 | 295245 |
| 11 | 885735 |
| 12 | 2657205 |
| 13 | 7971615 |
| 14 | 23914845 |
| 15 | 71744535 |
| 16 | 215233605 |
| 17 | 645700815 |
| 18 | 1937102445 |
| 19 | 5811307335 |
| 20 | 17433922005 |
| 21 | 52301766015 |
| 22 | 156905298045 |
| 23 | 470715894135 |
| 24 | 1412147682405 |
| 25 | 4236443047215 |
| 26 | 12709329141645 |