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 | -3 |
| 2 | 15 |
| 3 | -120 |
| 4 | 915 |
| 5 | -7086 |
| 6 | 56661 |
| 7 | -462405 |
| 8 | 3819165 |
| 9 | -31843110 |
| 10 | 267610443 |
| 11 | -2263491255 |
| 12 | 19246265025 |
| 13 | -164379723735 |
| 14 | 1409306287470 |
| 15 | -12122528944620 |
| 16 | 104575462390842 |
| 17 | -904411297029585 |
| 18 | 7839310835762475 |
| 19 | -68086561401745275 |
| 20 | 592417977205534017 |