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) |
|---|---|
| 1 | 9 |
| 2 | 51 |
| 3 | 231 |
| 4 | 975 |
| 5 | 3999 |
| 6 | 16191 |
| 7 | 65151 |
| 8 | 261375 |
| 9 | 1047039 |
| 10 | 4191231 |
| 11 | 16771071 |
| 12 | 67096575 |
| 13 | 268410879 |
| 14 | 1073692671 |
| 15 | 4294868991 |
| 16 | 17179672575 |
| 17 | 68719083519 |
| 18 | 274877120511 |
| 19 | 1099510054911 |
| 20 | 4398043365375 |
| 21 | 17592179752959 |
| 22 | 70368731594751 |
| 23 | 281474951544831 |
| 24 | 1125899856510975 |