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 | 1 |
| 2 | 2 |
| 3 | 0 |
| 4 | 12 |
| 5 | -160 |
| 6 | 3240 |
| 7 | -86688 |
| 8 | 2922640 |
| 9 | -119971584 |
| 10 | 5847901920 |
| 11 | -332122243200 |
| 12 | 21653202377664 |
| 13 | -1601381638172160 |
| 14 | 133036354347921024 |
| 15 | -12314128238585510400 |
| 16 | 1261212911036957548800 |
| 17 | -142082122642808666185728 |
| 18 | 17514853400850824425213440 |
| 19 | -2351847513553411263501035520 |
| 20 | 342599734607249938595012582400 |