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 | -8 |
| 2 | 56 |
| 3 | -400 |
| 4 | 2840 |
| 5 | -20208 |
| 6 | 143664 |
| 7 | -1021728 |
| 8 | 7265240 |
| 9 | -51665200 |
| 10 | 367392656 |
| 11 | -2612584928 |
| 12 | 18578329456 |
| 13 | -132112749920 |
| 14 | 939467783520 |
| 15 | -6680662171200 |
| 16 | 47506922377560 |
| 17 | -337827035002800 |
| 18 | 2402325467002320 |
| 19 | -17083203745473120 |
| 20 | 121480558396908240 |
| 21 | -863861754435010080 |