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 | -9 |
| 5 | 62 |
| 6 | -399 |
| 7 | 3048 |
| 8 | -26045 |
| 9 | 247298 |
| 10 | -2582027 |
| 11 | 29416876 |
| 12 | -363327081 |
| 13 | 4837734374 |
| 14 | -69105690039 |
| 15 | 1054490587824 |
| 16 | -17122237729589 |
| 17 | 294828907099274 |
| 18 | -5366869867749347 |
| 19 | 102988994579465716 |
| 20 | -2078107926978317889 |
| 21 | 43988545301378533742 |