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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 18 |
| 6 | 78 |
| 7 | 456 |
| 8 | 4299 |
| 9 | 68754 |
| 10 | 1990286 |
| 11 | 106088988 |
| 12 | 10454883132 |
| 13 | 1904236651216 |
| 14 | 641859005526860 |
| 15 | 401547534010157680 |
| 16 | 467956331904669136874 |
| 17 | 1019785644052109276678788 |
| 18 | 4171197546082606538129623140 |