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 | -35 |
| 5 | 325 |
| 6 | -1295 |
| 7 | -12455 |
| 8 | 283285 |
| 9 | -2186675 |
| 10 | -5612255 |
| 11 | 324564625 |
| 12 | -2869315163 |
| 13 | -12271744331 |
| 14 | 490525545169 |
| 15 | -2159646628535 |
| 16 | -58485623789483 |
| 17 | 634417586418781 |
| 18 | 8780962428445537 |
| 19 | -156001827155519807 |
| 20 | -2145519156372933275 |
| 21 | 50455156500263955781 |