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 | 0 |
| 2 | -3 |
| 3 | 9 |
| 4 | -24 |
| 5 | 60 |
| 6 | -84 |
| 7 | -756 |
| 8 | 13104 |
| 9 | -157248 |
| 10 | 1795248 |
| 11 | -20900880 |
| 12 | 254007936 |
| 13 | -3250473408 |
| 14 | 43922668608 |
| 15 | -626830626240 |
| 16 | 9437477107968 |
| 17 | -149644407564288 |
| 18 | 2493958878657792 |
| 19 | -43592393744250624 |
| 20 | 797394015216175104 |
| 21 | -15230735270523601920 |