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 | 0 |
| 2 | -1 |
| 3 | 1 |
| 4 | -7 |
| 5 | 31 |
| 6 | -281 |
| 7 | 2381 |
| 8 | -28015 |
| 9 | 346879 |
| 10 | -5149009 |
| 11 | 82769149 |
| 12 | -1499707991 |
| 13 | 29444151023 |
| 14 | -632715633577 |
| 15 | 14631547277101 |
| 16 | -364321853163871 |
| 17 | 9686058045625471 |
| 18 | -274387229080161569 |
| 19 | 8241211775883617405 |
| 20 | -261766195805536280839 |
| 21 | 8763341168691985628719 |