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 | -1 |
| 5 | 23 |
| 6 | -197 |
| 7 | 1093 |
| 8 | 5377 |
| 9 | -374863 |
| 10 | 9934889 |
| 11 | -195976201 |
| 12 | 2134159519 |
| 13 | 67270069831 |
| 14 | -6730482201869 |
| 15 | 365726633654957 |
| 16 | -15494292929032063 |
| 17 | 458469986808144737 |
| 18 | 2828723973314497873 |
| 19 | -2067360599320208561297 |
| 20 | 238687490584532161293631 |
| 21 | -20425982116564721266720009 |