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 | 0 |
| 2 | 1 |
| 3 | -3 |
| 4 | 8 |
| 5 | -30 |
| 6 | 136 |
| 7 | -693 |
| 8 | 3968 |
| 9 | -25260 |
| 10 | 176896 |
| 11 | -1351383 |
| 12 | 11184128 |
| 13 | -99680490 |
| 14 | 951878656 |
| 15 | -9695756073 |
| 16 | 104932671488 |
| 17 | -1202439837720 |
| 18 | 14544442556416 |
| 19 | -185185594118763 |
| 20 | 2475749026562048 |
| 21 | -34674437196568950 |