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 | 0 |
| 2 | 3 |
| 3 | -6 |
| 4 | 21 |
| 5 | -60 |
| 6 | 183 |
| 7 | -546 |
| 8 | 1641 |
| 9 | -4920 |
| 10 | 14763 |
| 11 | -44286 |
| 12 | 132861 |
| 13 | -398580 |
| 14 | 1195743 |
| 15 | -3587226 |
| 16 | 10761681 |
| 17 | -32285040 |
| 18 | 96855123 |
| 19 | -290565366 |
| 20 | 871696101 |
| 21 | -2615088300 |
| 22 | 7845264903 |
| 23 | -23535794706 |
| 24 | 70607384121 |
| 25 | -211822152360 |
| 26 | 635466457083 |
| 27 | -1906399371246 |