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 | 5 |
| 3 | -25 |
| 4 | 129 |
| 5 | -681 |
| 6 | 3653 |
| 7 | -19825 |
| 8 | 108545 |
| 9 | -598417 |
| 10 | 3317445 |
| 11 | -18474633 |
| 12 | 103274625 |
| 13 | -579168825 |
| 14 | 3256957317 |
| 15 | -18359266785 |
| 16 | 103706427393 |
| 17 | -586889743905 |
| 18 | 3326741166725 |
| 19 | -18885056428537 |
| 20 | 107347191941249 |
| 21 | -610916200215241 |