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 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 4920 |
| 8 | 37488 |
| 9 | 319644 |
| 10 | 3033264 |
| 11 | 31784280 |
| 12 | 364902480 |
| 13 | 4538652840 |
| 14 | 61102571376 |
| 15 | 885045657564 |
| 16 | 13722397569072 |
| 17 | 226742901078120 |
| 18 | 3977354871110160 |
| 19 | 73816786920489720 |
| 20 | 1444940702597713008 |
| 21 | 29750236302549282948 |