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 | -3 |
| 4 | 13 |
| 5 | -65 |
| 6 | 389 |
| 7 | -2723 |
| 8 | 21785 |
| 9 | -196065 |
| 10 | 1960649 |
| 11 | -21567139 |
| 12 | 258805669 |
| 13 | -3364473697 |
| 14 | 47102631757 |
| 15 | -706539476355 |
| 16 | 11304631621681 |
| 17 | -192178737568577 |
| 18 | 3459217276234385 |
| 19 | -65725128248453315 |
| 20 | 1314502564969066301 |