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 | -4 |
| 2 | -16 |
| 3 | -96 |
| 4 | -640 |
| 5 | -4480 |
| 6 | -32256 |
| 7 | -236544 |
| 8 | -1757184 |
| 9 | -13178880 |
| 10 | -99573760 |
| 11 | -756760576 |
| 12 | -5778898944 |
| 13 | -44304891904 |
| 14 | -340806860800 |
| 15 | -2629081497600 |
| 16 | -20331563581440 |
| 17 | -157569617756160 |
| 18 | -1223481737871360 |
| 19 | -9515969072332800 |
| 20 | -74124390668697600 |