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 | 2 |
| 3 | -1 |
| 4 | 19 |
| 5 | -1 |
| 6 | 304 |
| 7 | -81988 |
| 8 | 410857 |
| 9 | -249979 |
| 10 | 4165258 |
| 11 | -65721449 |
| 12 | 2562470143 |
| 13 | -5468849774 |
| 14 | 184344882947 |
| 15 | -137190436674212 |
| 16 | 10026981687881 |
| 17 | -12611493192339623 |
| 18 | 519973962150962777 |
| 19 | -8549627883788520181 |
| 20 | 1874648830674470878723 |
| 21 | -200643437220052588790575 |
| 22 | 877316785444551755504875 |