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 | 4 |
| 3 | -15 |
| 4 | 36 |
| 5 | -119 |
| 6 | 302 |
| 7 | -911 |
| 8 | 2440 |
| 9 | -7199 |
| 10 | 20186 |
| 11 | -60359 |
| 12 | 177204 |
| 13 | -546615 |
| 14 | 1683286 |
| 15 | -5401759 |
| 16 | 17456128 |
| 17 | -58447151 |
| 18 | 197925490 |
| 19 | -691264279 |
| 20 | 2446636396 |
| 21 | -8897012871 |
| 22 | 32811147054 |
| 23 | -123933345455 |
| 24 | 474792813176 |
| 25 | -1858243857599 |
| 26 | 7375013350282 |
| 27 | -29840434526951 |