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 | 1 |
| 4 | -23 |
| 5 | -149 |
| 6 | -539 |
| 7 | -1469 |
| 8 | 77281 |
| 9 | 911737 |
| 10 | 5657401 |
| 11 | 25134121 |
| 12 | -2065730039 |
| 13 | -35352993389 |
| 14 | -310739232803 |
| 15 | -1913714425349 |
| 16 | 213881558916481 |
| 17 | 4797269708789041 |
| 18 | 54560246286936241 |
| 19 | 429606655679843857 |
| 20 | -60718212515535701399 |
| 21 | -1684610587476711352709 |