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 | 2 |
| 5 | -11 |
| 6 | 61 |
| 7 | -281 |
| 8 | 1191 |
| 9 | -5923 |
| 10 | 41791 |
| 11 | -354091 |
| 12 | 2968021 |
| 13 | -24059751 |
| 14 | 204718515 |
| 15 | -1996937671 |
| 16 | 22125450621 |
| 17 | -258434553861 |
| 18 | 3056858429581 |
| 19 | -37181421375349 |
| 20 | 482010195953821 |
| 21 | -6741275765687821 |
| 22 | 99663246605243861 |
| 23 | -1521712424934601901 |