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 | 3 |
| 1 | 15 |
| 2 | 73 |
| 3 | 361 |
| 4 | 1806 |
| 5 | 9122 |
| 6 | 46425 |
| 7 | 237721 |
| 8 | 1223365 |
| 9 | 6321965 |
| 10 | 32784830 |
| 11 | 170528190 |
| 12 | 889291352 |
| 13 | 4648068192 |
| 14 | 24342384337 |
| 15 | 127707864849 |
| 16 | 671047979300 |
| 17 | 3531026714720 |
| 18 | 18603737992455 |
| 19 | 98129545962855 |
| 20 | 518149580437560 |