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) |
|---|---|
| 1 | 5 |
| 2 | -15 |
| 3 | 40 |
| 4 | -150 |
| 5 | 624 |
| 6 | -2620 |
| 7 | 11160 |
| 8 | -48750 |
| 9 | 217000 |
| 10 | -976872 |
| 11 | 4438920 |
| 12 | -20343700 |
| 13 | 93900240 |
| 14 | -435970980 |
| 15 | 2034504992 |
| 16 | -9536718750 |
| 17 | 44878791360 |
| 18 | -211927733500 |
| 19 | 1003867701480 |
| 20 | -4768371093720 |
| 21 | 22706531339280 |