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 | 2 |
| 2 | 1 |
| 3 | -3 |
| 4 | -6 |
| 5 | 6 |
| 6 | 36 |
| 7 | 0 |
| 8 | -252 |
| 9 | -252 |
| 10 | 2016 |
| 11 | 4536 |
| 12 | -17640 |
| 13 | -72072 |
| 14 | 157248 |
| 15 | 1166256 |
| 16 | -1192464 |
| 17 | -19852560 |
| 18 | 419328 |
| 19 | 357765408 |
| 20 | 349798176 |
| 21 | -6805509984 |
| 22 | -14151271680 |
| 23 | 135569947968 |
| 24 | 461049196608 |
| 25 | -2792629554624 |
| 26 | -14318859469824 |
| 27 | 58289508950400 |
| 28 | 444898714635648 |