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 | 3 |
| 4 | -4 |
| 5 | -50 |
| 6 | -36 |
| 7 | 2058 |
| 8 | 10800 |
| 9 | -131616 |
| 10 | -1975680 |
| 11 | 7741800 |
| 12 | 417480480 |
| 13 | 1307617584 |
| 14 | -101626746144 |
| 15 | -1284067345680 |
| 16 | 25419094122240 |
| 17 | 791333924647680 |
| 18 | -3900043588999680 |
| 19 | -472446912421801728 |
| 20 | -3183064994777932800 |