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 | 4 |
| 3 | 16 |
| 4 | 82 |
| 5 | 458 |
| 6 | 3228 |
| 7 | 24036 |
| 8 | 212448 |
| 9 | 2032992 |
| 10 | 21781440 |
| 11 | 246853440 |
| 12 | 3201742080 |
| 13 | 42580650240 |
| 14 | 621037186560 |
| 15 | 9664270963200 |
| 16 | 161166707251200 |
| 17 | 2781679603046400 |
| 18 | 52204357423411200 |
| 19 | 1004687538456268800 |
| 20 | 20823621371578368000 |
| 21 | 447027656835852288000 |