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 | 1 |
| 4 | -1 |
| 5 | 1 |
| 6 | -691 |
| 7 | 1 |
| 8 | -3617 |
| 9 | 43867 |
| 10 | -174611 |
| 11 | 77683 |
| 12 | -236364091 |
| 13 | 657931 |
| 14 | -3392780147 |
| 15 | 1723168255201 |
| 16 | -7709321041217 |
| 17 | 151628697551 |
| 18 | -26315271553053477373 |
| 19 | 154210205991661 |
| 20 | -261082718496449122051 |
| 21 | 1520097643918070802691 |