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 | -4 |
| 4 | -4 |
| 5 | 24 |
| 6 | 120 |
| 7 | -960 |
| 8 | -12096 |
| 9 | 120960 |
| 10 | 3024000 |
| 11 | -36288000 |
| 12 | -1576143360 |
| 13 | 22066007040 |
| 14 | 1525620096000 |
| 15 | -24409921536000 |
| 16 | -2522591034163200 |
| 17 | 45406638614937600 |
| 18 | 6686974460694528000 |
| 19 | -133739489213890560000 |
| 20 | -27033456071346536448000 |
| 21 | 594736033569623801856000 |