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 | 3 |
| 2 | 18 |
| 3 | 140 |
| 4 | 1260 |
| 5 | 12474 |
| 6 | 132132 |
| 7 | 1472328 |
| 8 | 17065620 |
| 9 | 204155380 |
| 10 | 2506399896 |
| 11 | 31443925968 |
| 12 | 401783498480 |
| 13 | 5215458874500 |
| 14 | 68633685693000 |
| 15 | 914099013896400 |
| 16 | 12304253831789700 |
| 17 | 167193096184907100 |
| 18 | 2291164651422801000 |
| 19 | 31637804708163654000 |
| 20 | 439903041116118980400 |