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 | 0 |
| 2 | 6 |
| 3 | 18 |
| 4 | 54 |
| 5 | 174 |
| 6 | 582 |
| 7 | 1974 |
| 8 | 6726 |
| 9 | 22950 |
| 10 | 78342 |
| 11 | 267462 |
| 12 | 913158 |
| 13 | 3117702 |
| 14 | 10644486 |
| 15 | 36342534 |
| 16 | 124081158 |
| 17 | 423639558 |
| 18 | 1446395910 |
| 19 | 4938304518 |
| 20 | 16860426246 |
| 21 | 57565095942 |
| 22 | 196539531270 |
| 23 | 671027933190 |
| 24 | 2291032670214 |
| 25 | 7822074814470 |
| 26 | 26706233917446 |
| 27 | 91180786040838 |