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 | 0 |
| 1 | 3 |
| 2 | -18 |
| 3 | 135 |
| 4 | -972 |
| 5 | 7047 |
| 6 | -51030 |
| 7 | 369603 |
| 8 | -2676888 |
| 9 | 19387755 |
| 10 | -140418522 |
| 11 | 1017000927 |
| 12 | -7365772260 |
| 13 | 53347641903 |
| 14 | -386377801758 |
| 15 | 2798395587675 |
| 16 | -20267773741872 |
| 17 | 146792202740307 |
| 18 | -1063163180118690 |
| 19 | 7700108905374903 |
| 20 | -55769122053317628 |
| 21 | 403915712468279895 |