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 | 3 |
| 4 | 8 |
| 5 | 30 |
| 6 | 720 |
| 7 | 210 |
| 8 | 40320 |
| 9 | 90720 |
| 10 | 1209600 |
| 11 | 226800 |
| 12 | 43545600 |
| 13 | 5241600 |
| 14 | 7925299200 |
| 15 | 14859936000 |
| 16 | 634023936000 |
| 17 | 8083805184000 |
| 18 | 582033973248000 |
| 19 | 115194223872000 |
| 20 | 221172909834240000 |
| 21 | 1161157776629760000 |