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 | -1 |
| 3 | 7 |
| 4 | -43 |
| 5 | 221 |
| 6 | -341 |
| 7 | -15980 |
| 8 | 370761 |
| 9 | -5688125 |
| 10 | 62689871 |
| 11 | -197586839 |
| 12 | -14973562979 |
| 13 | 585250669316 |
| 14 | -14306382821485 |
| 15 | 240985102271971 |
| 16 | -1121421968408303 |
| 17 | -122020498882279931 |
| 18 | 6674724196051810807 |
| 19 | -223424819176020519168 |
| 20 | 5051515662105879438501 |