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) |
|---|---|
| 3 | 1 |
| 4 | -5 |
| 5 | 55 |
| 6 | -385 |
| 7 | 3311 |
| 8 | -25585 |
| 9 | 208335 |
| 10 | -1652145 |
| 11 | 13275471 |
| 12 | -105970865 |
| 13 | 848699215 |
| 14 | -6785865905 |
| 15 | 54301841231 |
| 16 | -434355079345 |
| 17 | 3475079247695 |
| 18 | -27799679551665 |
| 19 | 222401254176591 |
| 20 | -1779194762447025 |
| 21 | 14233619183613775 |