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 | -4 |
| 4 | -5 |
| 5 | -21 |
| 6 | 59 |
| 7 | 184 |
| 8 | 1469 |
| 9 | -2515 |
| 10 | -44419 |
| 11 | -389004 |
| 12 | -677129 |
| 13 | 48209431 |
| 14 | 432521335 |
| 15 | 6727493744 |
| 16 | -202699840391 |
| 17 | -2757368732391 |
| 18 | -137883154808071 |
| 19 | 3024277973351020 |
| 20 | 134932587262253171 |
| 21 | 10064373238238267651 |