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 | -1 |
| 2 | -6 |
| 3 | 15 |
| 4 | 272 |
| 5 | -745 |
| 6 | -29976 |
| 7 | 61271 |
| 8 | 6065856 |
| 9 | -2723697 |
| 10 | -1941455080 |
| 11 | -3989345041 |
| 12 | 897021218400 |
| 13 | 4964061925511 |
| 14 | -562221881675832 |
| 15 | -5689641396555705 |
| 16 | 456732442022509184 |
| 17 | 7321841133968133023 |
| 18 | -464200472167634521800 |
| 19 | -10961686347887871324289 |
| 20 | 573373115861405030522400 |