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 | 2 |
| 2 | 1 |
| 3 | -1 |
| 4 | 19 |
| 5 | 149 |
| 6 | 683 |
| 7 | 2568 |
| 8 | 8801 |
| 9 | 28814 |
| 10 | 92262 |
| 11 | 292334 |
| 12 | 921812 |
| 13 | 2900518 |
| 14 | 9118183 |
| 15 | 28653193 |
| 16 | 90026155 |
| 17 | 282837225 |
| 18 | 888573621 |
| 19 | 2791553542 |
| 20 | 8769944569 |
| 21 | 27551617590 |
| 22 | 86555987697 |
| 23 | 271923687926 |
| 24 | 854273498233 |
| 25 | 2683779389671 |