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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 0 |
| 5 | -6 |
| 6 | -36 |
| 7 | -192 |
| 8 | -1104 |
| 9 | -7248 |
| 10 | -54816 |
| 11 | -472512 |
| 12 | -4573824 |
| 13 | -49064448 |
| 14 | -577130496 |
| 15 | -7381281792 |
| 16 | -101940854784 |
| 17 | -1511556077568 |
| 18 | -23945902043136 |
| 19 | -403579232182272 |
| 20 | -7209532170092544 |
| 21 | -136064164749017088 |
| 22 | -2705030337674674176 |
| 23 | -56501002847058788352 |