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 | 0 |
| 3 | 1 |
| 4 | -3 |
| 5 | 18 |
| 6 | -128 |
| 7 | 1132 |
| 8 | -11812 |
| 9 | 142342 |
| 10 | -1943608 |
| 11 | 29647946 |
| 12 | -499539274 |
| 13 | 9211833980 |
| 14 | -184511226396 |
| 15 | 3988612069192 |
| 16 | -92549005782872 |
| 17 | 2294158840990112 |
| 18 | -60504468236412688 |
| 19 | 1691556804706653840 |
| 20 | -49971227404392210528 |
| 21 | 1555373458584517657488 |