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 | 0 |
| 1 | 4 |
| 2 | 20 |
| 3 | 84 |
| 4 | 340 |
| 5 | 1364 |
| 6 | 5460 |
| 7 | 21844 |
| 8 | 87380 |
| 9 | 349524 |
| 10 | 1398100 |
| 11 | 5592404 |
| 12 | 22369620 |
| 13 | 89478484 |
| 14 | 357913940 |
| 15 | 1431655764 |
| 16 | 5726623060 |
| 17 | 22906492244 |
| 18 | 91625968980 |
| 19 | 366503875924 |
| 20 | 1466015503700 |
| 21 | 5864062014804 |
| 22 | 23456248059220 |
| 23 | 93824992236884 |
| 24 | 375299968947540 |
| 25 | 1501199875790164 |