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 | 11 |
| 3 | 55 |
| 4 | 239 |
| 5 | 991 |
| 6 | 4031 |
| 7 | 16255 |
| 8 | 65279 |
| 9 | 261631 |
| 10 | 1047551 |
| 11 | 4192255 |
| 12 | 16773119 |
| 13 | 67100671 |
| 14 | 268419071 |
| 15 | 1073709055 |
| 16 | 4294901759 |
| 17 | 17179738111 |
| 18 | 68719214591 |
| 19 | 274877382655 |
| 20 | 1099510579199 |
| 21 | 4398044413951 |
| 22 | 17592181850111 |
| 23 | 70368735789055 |