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 | 3 |
| 4 | -3 |
| 5 | 19 |
| 6 | -43 |
| 7 | 139 |
| 8 | -355 |
| 9 | 995 |
| 10 | -2587 |
| 11 | 6907 |
| 12 | -17939 |
| 13 | 46931 |
| 14 | -121419 |
| 15 | 314603 |
| 16 | -811203 |
| 17 | 2091459 |
| 18 | -5379963 |
| 19 | 13833179 |
| 20 | -35527795 |
| 21 | 91210035 |
| 22 | -234020267 |
| 23 | 600258507 |
| 24 | -1539135779 |
| 25 | 3945762211 |
| 26 | -10113490139 |
| 27 | 25918908603 |
| 28 | -66417608403 |
| 29 | 170182721299 |
| 30 | -436032111883 |
| 31 | 1117120911019 |