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 | 2 |
| 2 | -1 |
| 3 | 4 |
| 4 | -21 |
| 5 | 138 |
| 6 | -1091 |
| 7 | 10088 |
| 8 | -106918 |
| 9 | 1279220 |
| 10 | -17070418 |
| 11 | 251560472 |
| 12 | -4059954946 |
| 13 | 71250808916 |
| 14 | -1351381762990 |
| 15 | 27552372478592 |
| 16 | -601021307680207 |
| 17 | 13969016314470386 |
| 18 | -344653640328891233 |
| 19 | 8997206549370634644 |
| 20 | -247772400254700937149 |
| 21 | 7178881153198162073002 |