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 | -1 |
| 1 | -1 |
| 2 | 3 |
| 3 | 29 |
| 4 | 159 |
| 5 | 749 |
| 6 | 3303 |
| 7 | 14069 |
| 8 | 58719 |
| 9 | 241949 |
| 10 | 988503 |
| 11 | 4015109 |
| 12 | 16241679 |
| 13 | 65506349 |
| 14 | 263636103 |
| 15 | 1059360149 |
| 16 | 4251855039 |
| 17 | 17050597949 |
| 18 | 68331794103 |
| 19 | 273715121189 |
| 20 | 1096023794799 |
| 21 | 4387584060749 |
| 22 | 17560800790503 |
| 23 | 70274592610229 |
| 24 | 281192530396959 |
| 25 | 1125052584678749 |