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 | -252 |
| 3 | -6553 |
| 4 | -65520 |
| 5 | -390593 |
| 6 | -1679552 |
| 7 | -5764673 |
| 8 | -16776960 |
| 9 | -43046209 |
| 10 | -99998976 |
| 11 | -214356833 |
| 12 | -429977600 |
| 13 | -815722529 |
| 14 | -1475772672 |
| 15 | -2562857857 |
| 16 | -4294901760 |
| 17 | -6975626369 |
| 18 | -11019698432 |
| 19 | -16983038753 |
| 20 | -25598951424 |