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 | -4 |
| 3 | -20 |
| 4 | -140 |
| 5 | -1192 |
| 6 | -11656 |
| 7 | -127072 |
| 8 | -1517480 |
| 9 | -19624400 |
| 10 | -272656064 |
| 11 | -4046157472 |
| 12 | -63844717184 |
| 13 | -1067307017600 |
| 14 | -18846094327360 |
| 15 | -350578477836160 |
| 16 | -6854465726916640 |
| 17 | -140564170444594880 |
| 18 | -3017526392523529600 |
| 19 | -67690323794750627200 |