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 | -3 |
| 3 | 3 |
| 4 | 9 |
| 5 | 21 |
| 6 | -33 |
| 7 | -1173 |
| 8 | -13515 |
| 9 | -113739 |
| 10 | -532209 |
| 11 | 6284379 |
| 12 | 264830061 |
| 13 | 5897799141 |
| 14 | 104393462439 |
| 15 | 1459983940203 |
| 16 | 10308316834293 |
| 17 | -308010522508395 |
| 18 | -19576840707893409 |
| 19 | -726806556195360069 |
| 20 | -22261372611370303875 |
| 21 | -591210850189999983099 |