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 | 25 |
| 5 | 41 |
| 6 | -1049 |
| 7 | 2899 |
| 8 | 54545 |
| 9 | -610415 |
| 10 | -1363409 |
| 11 | 92652011 |
| 12 | -651996311 |
| 13 | -10663181255 |
| 14 | 262674487895 |
| 15 | -529402905149 |
| 16 | -68312606260319 |
| 17 | 1136414207246369 |
| 18 | 7701376416944095 |
| 19 | -584076369474366245 |
| 20 | 6461047290787787321 |
| 21 | 173442620419212050761 |