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 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 24 |
| 7 | 96 |
| 8 | 412 |
| 9 | 1607 |
| 10 | 6348 |
| 11 | 24580 |
| 12 | 96334 |
| 13 | 378569 |
| 14 | 1508220 |
| 15 | 6079720 |
| 16 | 24879878 |
| 17 | 103335386 |
| 18 | 436032901 |
| 19 | 1869019800 |
| 20 | 8139613977 |
| 21 | 36008825317 |
| 22 | 161794412893 |
| 23 | 738167013847 |
| 24 | 3418757243139 |
| 25 | 16068569129711 |
| 26 | 76622168743677 |
| 27 | 370571105669576 |
| 28 | 1817199912384794 |