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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | -1 |
| 4 | 10 |
| 5 | 4 |
| 6 | -384 |
| 7 | 818 |
| 8 | 29800 |
| 9 | -205200 |
| 10 | -3612000 |
| 11 | 56042832 |
| 12 | 556589232 |
| 13 | -19091774352 |
| 14 | -70128589608 |
| 15 | 8044430218680 |
| 16 | -25379500932864 |
| 17 | -4055729067351552 |
| 18 | 48310659088501248 |
| 19 | 2334746679051721536 |
| 20 | -58078273556262804480 |
| 21 | -1420062892415588203776 |