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 | 0 |
| 1 | 1 |
| 2 | -2 |
| 3 | 4 |
| 4 | -16 |
| 5 | 96 |
| 6 | -576 |
| 7 | 3760 |
| 8 | -30080 |
| 9 | 278656 |
| 10 | -2786560 |
| 11 | 30298368 |
| 12 | -363580416 |
| 13 | 4748913664 |
| 14 | -66484791296 |
| 15 | 995368112128 |
| 16 | -15925889794048 |
| 17 | 270949991841792 |
| 18 | -4877099853152256 |
| 19 | 92635808324780032 |
| 20 | -1852716166495600640 |