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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | -17 |
| 5 | 31 |
| 6 | -691 |
| 7 | 5461 |
| 8 | -929569 |
| 9 | 3202291 |
| 10 | -221930581 |
| 11 | 4722116521 |
| 12 | -968383680827 |
| 13 | 14717667114151 |
| 14 | -2093660879252671 |
| 15 | 86125672563201181 |
| 16 | -129848163681107301953 |
| 17 | 868320396104950823611 |
| 18 | -209390615747646519456961 |
| 19 | 14129659550745551130667441 |
| 20 | -8486725345098385062639014237 |