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 | 2 |
| 2 | -2 |
| 3 | 4 |
| 4 | -12 |
| 5 | 40 |
| 6 | -144 |
| 7 | 544 |
| 8 | -2128 |
| 9 | 8544 |
| 10 | -35008 |
| 11 | 145792 |
| 12 | -615296 |
| 13 | 2625792 |
| 14 | -11311616 |
| 15 | 49124352 |
| 16 | -214838528 |
| 17 | 945350144 |
| 18 | -4182412288 |
| 19 | 18593224704 |
| 20 | -83015133184 |
| 21 | 372090122240 |
| 22 | -1673660915712 |
| 23 | 7552262979584 |
| 24 | -34178799378432 |
| 25 | 155096251351040 |
| 26 | -705533929816064 |