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 | 1 |
| 2 | 3 |
| 3 | 7 |
| 4 | 21 |
| 5 | 57 |
| 6 | 171 |
| 7 | 495 |
| 8 | 1485 |
| 9 | 4401 |
| 10 | 13203 |
| 11 | 39447 |
| 12 | 118341 |
| 13 | 354537 |
| 14 | 1063611 |
| 15 | 3189375 |
| 16 | 9568125 |
| 17 | 28700001 |
| 18 | 86100003 |
| 19 | 258286887 |
| 20 | 774860661 |
| 21 | 2324542617 |
| 22 | 6973627851 |
| 23 | 20920765455 |
| 24 | 62762296365 |
| 25 | 188286534801 |
| 26 | 564859604403 |
| 27 | 1694577750327 |
| 28 | 5083733250981 |
| 29 | 15251196564297 |
| 30 | 45753589692891 |