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 | -1 |
| 3 | -1 |
| 4 | 2 |
| 5 | 49 |
| 6 | 629 |
| 7 | 6961 |
| 8 | 38366 |
| 9 | -1899687 |
| 10 | -133065253 |
| 11 | -6482111309 |
| 12 | -281940658286 |
| 13 | -10702380933551 |
| 14 | -247708227641863 |
| 15 | 14512103549430397 |
| 16 | 3377044611825908414 |
| 17 | 433180638973276282801 |
| 18 | 47474992085447610990231 |