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 | 0 |
| 2 | 2 |
| 3 | -3 |
| 4 | 16 |
| 5 | -80 |
| 6 | 440 |
| 7 | -3171 |
| 8 | 24680 |
| 9 | -218952 |
| 10 | 2170018 |
| 11 | -23566675 |
| 12 | 279907076 |
| 13 | -3603250716 |
| 14 | 49968204078 |
| 15 | -742893013695 |
| 16 | 11785962447792 |
| 17 | -198748512229968 |
| 18 | 3550002639307890 |
| 19 | -66954457199954115 |
| 20 | 1329661510693923636 |