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 | -1 |
| 3 | -5 |
| 4 | -13 |
| 5 | -149 |
| 6 | -1861 |
| 7 | -21965 |
| 8 | -267373 |
| 9 | -3163109 |
| 10 | -34739221 |
| 11 | -352104125 |
| 12 | -3806609533 |
| 13 | -67068890069 |
| 14 | -1866226978981 |
| 15 | -51776974365485 |
| 16 | -1180415240484493 |
| 17 | -19613026052409029 |
| 18 | -122604194898649141 |
| 19 | 6950364605049945955 |
| 20 | 394565422299921179747 |
| 21 | 13840685990526765512011 |