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 | -20 |
| 2 | 170 |
| 3 | -800 |
| 4 | 2415 |
| 5 | -6404 |
| 6 | 21550 |
| 7 | -71080 |
| 8 | 178295 |
| 9 | -419200 |
| 10 | 1203282 |
| 11 | -3294360 |
| 12 | 7476320 |
| 13 | -17381780 |
| 14 | 44919500 |
| 15 | -107605880 |
| 16 | 237628435 |
| 17 | -544086720 |
| 18 | 1273805460 |
| 19 | -2864694880 |
| 20 | 6256648862 |
| 21 | -13710129840 |