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 | 1 |
| 3 | -4 |
| 4 | -2 |
| 5 | 274 |
| 6 | -3442 |
| 7 | -12552 |
| 8 | 2108664 |
| 9 | -63083232 |
| 10 | 87416112 |
| 11 | 112192496976 |
| 12 | -7487840132544 |
| 13 | 174521224997040 |
| 14 | 19793498724358032 |
| 15 | -3109195219736188416 |
| 16 | 209306170972547346816 |
| 17 | 2973238556525799866496 |
| 18 | -3013574861684426837113728 |
| 19 | 456220653756733889826621696 |