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 | -5 |
| 5 | 23 |
| 6 | 53 |
| 7 | -593 |
| 8 | -5165 |
| 9 | 110123 |
| 10 | 231743 |
| 11 | -8113223 |
| 12 | -33497425 |
| 13 | 1744764499 |
| 14 | 3563384029 |
| 15 | -258115578289 |
| 16 | -4191097954685 |
| 17 | 402402297433523 |
| 18 | 813628574192123 |
| 19 | -99925014024526283 |
| 20 | -403078530716889835 |
| 21 | 61606956815080291849 |