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 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 105 |
| 5 | 1470 |
| 6 | 42630 |
| 7 | 1364160 |
| 8 | 75028800 |
| 9 | 3676411200 |
| 10 | 272054428800 |