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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 2 |
| 4 | -8 |
| 5 | 31 |
| 6 | -136 |
| 7 | 692 |
| 8 | -3968 |
| 9 | 25261 |
| 10 | -176896 |
| 11 | 1351382 |
| 12 | -11184128 |
| 13 | 99680491 |
| 14 | -951878656 |
| 15 | 9695756072 |
| 16 | -104932671488 |
| 17 | 1202439837721 |
| 18 | -14544442556416 |
| 19 | 185185594118762 |
| 20 | -2475749026562048 |
| 21 | 34674437196568951 |