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 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | -12 |
| 4 | -140 |
| 5 | 420 |
| 6 | 13692 |
| 7 | -23744 |
| 8 | -2366784 |
| 9 | 126000 |
| 10 | 641927440 |
| 11 | 1306329024 |
| 12 | -252172135488 |
| 13 | -1138135788608 |
| 14 | 135593735484480 |
| 15 | 999117715814400 |
| 16 | -95707279587325952 |
| 17 | -1013737882826462976 |
| 18 | 85873512374909086464 |
| 19 | 1217682899871358735360 |
| 20 | -95486742904897158097920 |