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 | 1 |
| 3 | -5 |
| 4 | 23 |
| 5 | -119 |
| 6 | 619 |
| 7 | -4759 |
| 8 | 48145 |
| 9 | -476657 |
| 10 | 4249961 |
| 11 | -48286061 |
| 12 | 691331431 |
| 13 | -9132207655 |
| 14 | 117900772963 |
| 15 | -2025161870159 |
| 16 | 37607411624609 |
| 17 | -628236985455329 |
| 18 | 10768798391659345 |
| 19 | -215626810984559317 |
| 20 | 4751529623277906871 |
| 21 | -105427459848063440471 |