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 | -2 |
| 2 | 2 |
| 3 | -4 |
| 4 | 2 |
| 5 | -12 |
| 6 | -12 |
| 7 | -72 |
| 8 | -190 |
| 9 | -700 |
| 10 | -2308 |
| 11 | -8120 |
| 12 | -28364 |
| 13 | -100856 |
| 14 | -360792 |
| 15 | -1301904 |
| 16 | -4727358 |
| 17 | -17268636 |
| 18 | -63405012 |
| 19 | -233885784 |
| 20 | -866327748 |
| 21 | -3220976616 |
| 22 | -12016209192 |
| 23 | -44966763504 |
| 24 | -168750724428 |
| 25 | -634935132312 |
| 26 | -2394717424552 |
| 27 | -9051945482032 |