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 | -5 |
| 4 | 18 |
| 5 | -60 |
| 6 | 189 |
| 7 | -601 |
| 8 | 1967 |
| 9 | -6544 |
| 10 | 21872 |
| 11 | -73247 |
| 12 | 246080 |
| 13 | -829924 |
| 14 | 2808357 |
| 15 | -9527485 |
| 16 | 32389671 |
| 17 | -110316862 |
| 18 | 376372802 |
| 19 | -1286063899 |
| 20 | 4400499380 |
| 21 | -15075608840 |
| 22 | 51704898623 |
| 23 | -177513230200 |
| 24 | 610007283817 |
| 25 | -2098029341745 |
| 26 | 7221561430933 |
| 27 | -24875274224531 |