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 | 3 |
| 3 | -3 |
| 4 | 81 |
| 5 | 315 |
| 6 | -765 |
| 7 | 4725 |
| 8 | 16065 |
| 9 | 1091475 |
| 10 | 10843875 |
| 11 | -65956275 |
| 12 | 770425425 |
| 13 | 5892561675 |
| 14 | -6512831325 |
| 15 | 213901813125 |
| 16 | 47691165146625 |
| 17 | 1318815779155875 |
| 18 | -7354191439720125 |
| 19 | 223312383805636125 |
| 20 | 2055628831852220625 |