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 | -1 |
| 3 | 5 |
| 4 | -25 |
| 5 | 141 |
| 6 | -849 |
| 7 | 5349 |
| 8 | -34825 |
| 9 | 232445 |
| 10 | -1582081 |
| 11 | 10938709 |
| 12 | -76616249 |
| 13 | 542472685 |
| 14 | -3876400305 |
| 15 | 27919883205 |
| 16 | -202480492905 |
| 17 | 1477306676445 |
| 18 | -10836099051105 |
| 19 | 79861379898165 |
| 20 | -591082795606425 |