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 | 3 |
| 2 | 7 |
| 3 | 21 |
| 4 | 45 |
| 5 | 135 |
| 6 | 291 |
| 7 | 873 |
| 8 | 1881 |
| 9 | 5643 |
| 10 | 12159 |
| 11 | 36477 |
| 12 | 78597 |
| 13 | 235791 |
| 14 | 508059 |
| 15 | 1524177 |
| 16 | 3284145 |
| 17 | 9852435 |
| 18 | 21229047 |
| 19 | 63687141 |
| 20 | 137226717 |
| 21 | 411680151 |
| 22 | 887047443 |
| 23 | 2661142329 |
| 24 | 5733964809 |
| 25 | 17201894427 |
| 26 | 37064931183 |
| 27 | 111194793549 |
| 28 | 239591481525 |
| 29 | 718774444575 |