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 | 2 |
| 3 | 2 |
| 4 | 8 |
| 5 | 20 |
| 6 | 68 |
| 7 | 206 |
| 8 | 692 |
| 9 | 2306 |
| 10 | 7930 |
| 11 | 27492 |
| 12 | 96792 |
| 13 | 343670 |
| 14 | 1231932 |
| 15 | 4447510 |
| 16 | 16164914 |
| 17 | 59086618 |
| 18 | 217091832 |
| 19 | 801247614 |
| 20 | 2969432270 |
| 21 | 11045446688 |
| 22 | 41224168020 |
| 23 | 154329373022 |
| 24 | 579377940390 |
| 25 | 2180684278698 |
| 26 | 8227240466520 |
| 27 | 31107755899600 |