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 | 2 |
| 3 | -5 |
| 4 | 15 |
| 5 | -52 |
| 6 | 203 |
| 7 | -877 |
| 8 | 4140 |
| 9 | -21147 |
| 10 | 115975 |
| 11 | -678570 |
| 12 | 4213597 |
| 13 | -27644437 |
| 14 | 190899322 |
| 15 | -1382958545 |
| 16 | 10480142147 |
| 17 | -82864869804 |
| 18 | 682076806159 |
| 19 | -5832742205057 |
| 20 | 51724158235372 |
| 21 | -474869816156751 |
| 22 | 4506715738447323 |
| 23 | -44152005855084346 |