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 | 0 |
| 2 | 0 |
| 3 | -6 |
| 4 | 0 |
| 5 | 0 |
| 6 | 360 |
| 7 | -5040 |
| 8 | 0 |
| 9 | -60480 |
| 10 | 3628800 |
| 11 | -39916800 |
| 12 | 19958400 |
| 13 | -3113510400 |
| 14 | 130767436800 |
| 15 | -1318571654400 |
| 16 | 3487131648000 |
| 17 | -355687428096000 |
| 18 | 12813639597158400 |
| 19 | -126713646259200000 |
| 20 | 1013709170073600000 |
| 21 | -85161707377883136000 |
| 22 | 2819368492175499264000 |