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 | 6 |
| 4 | -21 |
| 5 | 80 |
| 6 | -320 |
| 7 | 1326 |
| 8 | -5637 |
| 9 | 24434 |
| 10 | -107542 |
| 11 | 479196 |
| 12 | -2157045 |
| 13 | 9792702 |
| 14 | -44780606 |
| 15 | 206055345 |
| 16 | -953305628 |
| 17 | 4431463845 |
| 18 | -20686696836 |
| 19 | 96931500441 |
| 20 | -455722376856 |
| 21 | 2149086834269 |
| 22 | -10162544424168 |
| 23 | 48176923110789 |
| 24 | -228913128188293 |
| 25 | 1089973053510359 |