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 | -2 |
| 3 | -6 |
| 4 | -20 |
| 5 | -92 |
| 6 | -554 |
| 7 | -4002 |
| 8 | -33096 |
| 9 | -306440 |
| 10 | -3135766 |
| 11 | -35134670 |
| 12 | -427878628 |
| 13 | -5628940084 |
| 14 | -79572364498 |
| 15 | -1203168642362 |
| 16 | -19379896959776 |
| 17 | -331331041788640 |
| 18 | -5993029816637262 |
| 19 | -114348894263852326 |
| 20 | -2295445815821635932 |
| 21 | -48362099044178487564 |