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 | 3 |
| 2 | -6 |
| 3 | 39 |
| 4 | -213 |
| 5 | 1425 |
| 6 | -9681 |
| 7 | 69393 |
| 8 | -509307 |
| 9 | 3827856 |
| 10 | -29254443 |
| 11 | 226787682 |
| 12 | -1778491446 |
| 13 | 14084085711 |
| 14 | -112462798281 |
| 15 | 904485811944 |
| 16 | -7319902809228 |
| 17 | 59565238152789 |
| 18 | -487071807495099 |
| 19 | 4000169922457260 |
| 20 | -32980470088198209 |
| 21 | 272875134913543488 |