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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | 1 |
| 5 | -7 |
| 6 | -13 |
| 7 | 115 |
| 8 | 5657 |
| 9 | -50759 |
| 10 | -2129735 |
| 11 | 14303129 |
| 12 | 567824371 |
| 13 | -668626477 |
| 14 | -2536766233351 |
| 15 | -22685437440167 |
| 16 | 6386546752479769 |
| 17 | 164094712558603577 |
| 18 | -8391397652598907629 |
| 19 | -441809873725219477581 |
| 20 | 29040435128150468206405 |
| 21 | 2814195975064870847100773 |