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 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 24 |
| 6 | -24 |
| 7 | -120 |
| 8 | -720 |
| 9 | -5040 |
| 10 | 32256 |
| 11 | 169344 |
| 12 | 743040 |
| 13 | -380160 |
| 14 | -91048320 |
| 15 | -408710016 |
| 16 | -174230784 |
| 17 | 29842525440 |
| 18 | 455765667840 |
| 19 | 1061427732480 |
| 20 | -18914141343744 |
| 21 | -379628241094656 |
| 22 | -3305984467691520 |
| 23 | 10588546824468480 |
| 24 | 458522651844956160 |
| 25 | 5722461010387021824 |