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 | 1 |
| 3 | 10 |
| 4 | 10 |
| 5 | 604 |
| 6 | -1844 |
| 7 | 107344 |
| 8 | -1201400 |
| 9 | 42193576 |
| 10 | -875584376 |
| 11 | 29853569008 |
| 12 | -880141783184 |
| 13 | 32865860907424 |
| 14 | -1216481572723616 |
| 15 | 51296026356128512 |
| 16 | -2244334822166729600 |
| 17 | 106984479644794783360 |
| 18 | -5358207684820194270080 |
| 19 | 286466413246622566048000 |