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 | 2 |
| 3 | 0 |
| 4 | -24 |
| 5 | -220 |
| 6 | -1200 |
| 7 | -2576 |
| 8 | 52864 |
| 9 | 1016208 |
| 10 | 10909440 |
| 11 | 57039488 |
| 12 | -687971328 |
| 13 | -26190716864 |
| 14 | -450123634688 |
| 15 | -4238375059200 |
| 16 | 24514848522240 |
| 17 | 2156422420074752 |
| 18 | 54984136073084928 |
| 19 | 799573460292407296 |
| 20 | 42320889956270080 |
| 21 | -425007017470737816576 |
| 22 | -15563879892284330213376 |