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 | 0 |
| 3 | -4 |
| 4 | -4 |
| 5 | 60 |
| 6 | 160 |
| 7 | -2000 |
| 8 | -9840 |
| 9 | 118160 |
| 10 | 915200 |
| 11 | -10900800 |
| 12 | -121640000 |
| 13 | 1448075200 |
| 14 | 22005235200 |
| 15 | -261817504000 |
| 16 | -5212995424000 |
| 17 | 61812285600000 |
| 18 | 1568367963136000 |
| 19 | -18458812571264000 |
| 20 | -584639647263360000 |