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 | 4 |
| 4 | 0 |
| 5 | 45 |
| 6 | -155 |
| 7 | 1748 |
| 8 | -13496 |
| 9 | 151169 |
| 10 | -1682191 |
| 11 | 22018412 |
| 12 | -307464872 |
| 13 | 4746159613 |
| 14 | -78744546907 |
| 15 | 1410956472396 |
| 16 | -27026759291728 |
| 17 | 552443153007777 |
| 18 | -11988735452427903 |
| 19 | 275451486233018100 |
| 20 | -6677966707663119664 |