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 | -2 |
| 4 | 10 |
| 5 | -20 |
| 6 | -16 |
| 7 | 488 |
| 8 | -4080 |
| 9 | 22160 |
| 10 | -7936 |
| 11 | -1616672 |
| 12 | 22996480 |
| 13 | -172976960 |
| 14 | -22368256 |
| 15 | 25518205568 |
| 16 | -485458114560 |
| 17 | 4964227109120 |
| 18 | -209865342976 |
| 19 | -1231298393825792 |
| 20 | 29816107240652800 |
| 21 | -379260096755225600 |