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 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 6 |
| 5 | 18 |
| 6 | 46 |
| 7 | 132 |
| 8 | 408 |
| 9 | 1254 |
| 10 | 4110 |
| 11 | 13440 |
| 12 | 46420 |
| 13 | 160428 |
| 14 | 572706 |
| 15 | 2057252 |
| 16 | 7544784 |
| 17 | 27882252 |
| 18 | 104455308 |
| 19 | 394319118 |
| 20 | 1503100560 |
| 21 | 5768874688 |
| 22 | 22304692368 |
| 23 | 86749353342 |
| 24 | 339380104380 |
| 25 | 1334443604172 |
| 26 | 5272470030306 |