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) |
|---|---|
| 1 | 1 |
| 2 | -1 |
| 3 | 4 |
| 4 | -12 |
| 5 | 52 |
| 6 | -256 |
| 7 | 1502 |
| 8 | -10158 |
| 9 | 78360 |
| 10 | -680280 |
| 11 | 6574872 |
| 12 | -70075416 |
| 13 | 816909816 |
| 14 | -10342968456 |
| 15 | 141357740736 |
| 16 | -2074340369088 |
| 17 | 32530886655168 |
| 18 | -542971977209760 |
| 19 | 9610316495698416 |
| 20 | -179788450082431536 |
| 21 | 3544714566466060032 |