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 | 2 |
| 3 | -7 |
| 4 | 31 |
| 5 | -171 |
| 6 | 1141 |
| 7 | -8863 |
| 8 | 78653 |
| 9 | -785557 |
| 10 | 8716861 |
| 11 | -106395741 |
| 12 | 1416724915 |
| 13 | -20436548575 |
| 14 | 317477947151 |
| 15 | -5284248213091 |
| 16 | 93816998697721 |
| 17 | -1769737117839849 |
| 18 | 35347571931577609 |
| 19 | -745232024035027225 |
| 20 | 16538641134235561631 |
| 21 | -385387334950748244451 |