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 | 0 |
| 4 | -3 |
| 5 | -9 |
| 6 | -9 |
| 7 | 36 |
| 8 | 225 |
| 9 | 477 |
| 10 | -819 |
| 11 | -10944 |
| 12 | -37179 |
| 13 | 16875 |
| 14 | 870507 |
| 15 | 4253796 |
| 16 | 2481921 |
| 17 | -101978919 |
| 18 | -680495175 |
| 19 | -1060229088 |
| 20 | 16378166061 |
| 21 | 145672249311 |
| 22 | 368320357791 |
| 23 | -3415036002300 |
| 24 | -40270115077983 |
| 25 | -141926533828299 |
| 26 | 882584266861701 |
| 27 | 13970371667206176 |