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 | -1 |
| 3 | -4 |
| 4 | 9 |
| 5 | 52 |
| 6 | -175 |
| 7 | -1370 |
| 8 | 5985 |
| 9 | 60216 |
| 10 | -320063 |
| 11 | -3929550 |
| 12 | 24549745 |
| 13 | 354693796 |
| 14 | -2543955167 |
| 15 | -42233123938 |
| 16 | 341610526145 |
| 17 | 6404634620016 |
| 18 | -57626692351871 |
| 19 | -1203767371104790 |
| 20 | 11918048043239377 |
| 21 | 274395314816604636 |