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 | -1 |
| 3 | 5 |
| 4 | -12 |
| 5 | 109 |
| 6 | -405 |
| 7 | 4913 |
| 8 | -24976 |
| 9 | 372633 |
| 10 | -2419425 |
| 11 | 42646845 |
| 12 | -338219244 |
| 13 | 6863821509 |
| 14 | -64452230661 |
| 15 | 1478191260393 |
| 16 | -16062969072000 |
| 17 | 410493211996977 |
| 18 | -5072547848554017 |
| 19 | 142840036992492789 |
| 20 | -1979718755185227180 |