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) |
|---|---|
| 1 | -1 |
| 2 | 4 |
| 3 | -23 |
| 4 | 223 |
| 5 | -2800 |
| 6 | 42599 |
| 7 | -763220 |
| 8 | 15734388 |
| 9 | -366715248 |
| 10 | 9533820200 |
| 11 | -273549419552 |
| 12 | 8586984241870 |
| 13 | -292755986184548 |
| 14 | 10772849584162694 |
| 15 | -425587711650564816 |
| 16 | 17966217346985801150 |
| 17 | -807152054953801845760 |
| 18 | 38451365602113718874568 |
| 19 | -1936082850634342992601636 |