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 | 1 |
| 2 | 2 |
| 3 | 9 |
| 4 | 44 |
| 5 | 270 |
| 6 | 2064 |
| 7 | 17682 |
| 8 | 171296 |
| 9 | 1867968 |
| 10 | 22470840 |
| 11 | 294493320 |
| 12 | 4195969392 |
| 13 | 64416698112 |
| 14 | 1059685905264 |
| 15 | 18609306423120 |
| 16 | 347179119075840 |
| 17 | 6855335163907200 |
| 18 | 142889687354283264 |
| 19 | 3133647091691585280 |
| 20 | 72124075333003155840 |
| 21 | 1738384773846440146560 |