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 | 5 |
| 2 | 19 |
| 3 | 71 |
| 4 | 271 |
| 5 | 1055 |
| 6 | 4159 |
| 7 | 16511 |
| 8 | 65791 |
| 9 | 262655 |
| 10 | 1049599 |
| 11 | 4196351 |
| 12 | 16781311 |
| 13 | 67117055 |
| 14 | 268451839 |
| 15 | 1073774591 |
| 16 | 4295032831 |
| 17 | 17180000255 |
| 18 | 68719738879 |
| 19 | 274878431231 |
| 20 | 1099512676351 |
| 21 | 4398048608255 |
| 22 | 17592190238719 |