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 | -1 |
| 2 | 1 |
| 3 | -17 |
| 4 | 31 |
| 5 | -691 |
| 6 | 5461 |
| 7 | -929569 |
| 8 | 3202291 |
| 9 | -221930581 |
| 10 | 4722116521 |
| 11 | -56963745931 |
| 12 | 14717667114151 |
| 13 | -2093660879252671 |
| 14 | 86125672563201181 |
| 15 | -129848163681107301953 |
| 16 | 868320396104950823611 |
| 17 | -209390615747646519456961 |
| 18 | 14129659550745551130667441 |