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 | -4 |
| 2 | 24 |
| 3 | -160 |
| 4 | 1120 |
| 5 | -8064 |
| 6 | 59136 |
| 7 | -439296 |
| 8 | 3294720 |
| 9 | -24893440 |
| 10 | 189190144 |
| 11 | -1444724736 |
| 12 | 11076222976 |
| 13 | -85201715200 |
| 14 | 657270374400 |
| 15 | -5082890895360 |
| 16 | 39392404439040 |
| 17 | -305870434467840 |
| 18 | 2378992268083200 |
| 19 | -18531097667174400 |
| 20 | 144542561803960320 |
| 21 | -1128808577897594880 |