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 | 89 |
| 6 | -345 |
| 7 | 3093 |
| 8 | -17136 |
| 9 | 182097 |
| 10 | -1334025 |
| 11 | 16371365 |
| 12 | -150969324 |
| 13 | 2101489961 |
| 14 | -23556117585 |
| 15 | 367038504693 |
| 16 | -4870660226880 |
| 17 | 84100519126561 |
| 18 | -1293871061371761 |
| 19 | 24562906630580293 |
| 20 | -430689316852061740 |