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 | -508 |
| 3 | -19675 |
| 4 | -262128 |
| 5 | -1953093 |
| 6 | -10077632 |
| 7 | -40353479 |
| 8 | -134217472 |
| 9 | -387419977 |
| 10 | -999998976 |
| 11 | -2357945643 |
| 12 | -5159776256 |
| 13 | -10604491181 |
| 14 | -20661030400 |
| 15 | -38443326607 |
| 16 | -68719411200 |
| 17 | -118587745425 |
| 18 | -198359028224 |
| 19 | -322687173491 |
| 20 | -511998951424 |
| 21 | -794277949429 |