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 | -7 |
| 4 | 25 |
| 5 | -181 |
| 6 | 1201 |
| 7 | -10291 |
| 8 | 97777 |
| 9 | -1013545 |
| 10 | 12202561 |
| 11 | -151573951 |
| 12 | 2173233481 |
| 13 | -31758579997 |
| 14 | 524057015665 |
| 15 | -8838296029291 |
| 16 | 164416415570401 |
| 17 | -3145357419120721 |
| 18 | 65057767274601217 |
| 19 | -1391243470549894135 |
| 20 | 31671795881695430521 |
| 21 | -747996624368605997701 |