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 | 3 |
| 3 | -9 |
| 4 | 37 |
| 5 | -185 |
| 6 | 1111 |
| 7 | -7777 |
| 8 | 62217 |
| 9 | -559953 |
| 10 | 5599531 |
| 11 | -61594841 |
| 12 | 739138093 |
| 13 | -9608795209 |
| 14 | 134523132927 |
| 15 | -2017846993905 |
| 16 | 32285551902481 |
| 17 | -548854382342177 |
| 18 | 9879378882159187 |
| 19 | -187708198761024553 |
| 20 | 3754163975220491061 |