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 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 0 |
| 5 | 20 |
| 6 | -85 |
| 7 | 637 |
| 8 | -5096 |
| 9 | 46944 |
| 10 | -484401 |
| 11 | 5544341 |
| 12 | -69697672 |
| 13 | 954728788 |
| 14 | -14155260197 |
| 15 | 225856326165 |
| 16 | -3858874322928 |
| 17 | 70293211672352 |
| 18 | -1359957800892673 |
| 19 | 27849583539856909 |
| 20 | -601828107666316064 |