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 | 6 |
| 4 | 48 |
| 5 | 360 |
| 6 | 2880 |
| 7 | 25200 |
| 8 | 282240 |
| 9 | 3628800 |
| 10 | 50803200 |
| 11 | 758419200 |
| 12 | 12454041600 |
| 13 | 224172748800 |
| 14 | 4358914560000 |
| 15 | 90229531392000 |
| 16 | 1987665039360000 |
| 17 | 46595053080576000 |
| 18 | 1158829640736768000 |
| 19 | 30411275102208000000 |
| 20 | 839351192820940800000 |
| 21 | 24319288473733693440000 |