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 | -7 |
| 2 | 45 |
| 3 | -291 |
| 4 | 1881 |
| 5 | -12159 |
| 6 | 78597 |
| 7 | -508059 |
| 8 | 3284145 |
| 9 | -21229047 |
| 10 | 137226717 |
| 11 | -887047443 |
| 12 | 5733964809 |
| 13 | -37064931183 |
| 14 | 239591481525 |
| 15 | -1548743682699 |
| 16 | 10011236540769 |
| 17 | -64713650292711 |
| 18 | 418315611378573 |
| 19 | -2704034619149571 |
| 20 | 17479154549033145 |
| 21 | -112987031151647583 |