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 | -4 |
| 3 | 16 |
| 4 | -84 |
| 5 | 496 |
| 6 | -3140 |
| 7 | 20832 |
| 8 | -142932 |
| 9 | 1005856 |
| 10 | -7220100 |
| 11 | 52657392 |
| 12 | -389088084 |
| 13 | 2906551440 |
| 14 | -21914464708 |
| 15 | 166548194240 |
| 16 | -1274531623764 |
| 17 | 9812792232768 |
| 18 | -75955668337412 |
| 19 | 590742300208848 |
| 20 | -4614140648464980 |
| 21 | 36178872976542768 |
| 22 | -284664427193774916 |