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 | 4 |
| 3 | 20 |
| 4 | 72 |
| 5 | 232 |
| 6 | 716 |
| 7 | 2172 |
| 8 | 6544 |
| 9 | 19664 |
| 10 | 59028 |
| 11 | 177124 |
| 12 | 531416 |
| 13 | 1594296 |
| 14 | 4782940 |
| 15 | 14348876 |
| 16 | 43046688 |
| 17 | 129140128 |
| 18 | 387420452 |
| 19 | 1162261428 |
| 20 | 3486784360 |
| 21 | 10460353160 |
| 22 | 31381059564 |
| 23 | 94143178780 |
| 24 | 282429536432 |
| 25 | 847288609392 |