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 | 0 |
| 4 | -4 |
| 5 | 22 |
| 6 | -98 |
| 7 | 508 |
| 8 | -2952 |
| 9 | 21040 |
| 10 | -169360 |
| 11 | 1579168 |
| 12 | -16208784 |
| 13 | 185045936 |
| 14 | -2290934384 |
| 15 | 30842081632 |
| 16 | -445643595776 |
| 17 | 6905128910976 |
| 18 | -113892295743104 |
| 19 | 1995421707848192 |
| 20 | -36964967819409152 |
| 21 | 722345322667829760 |
| 22 | -14842592110869541888 |