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 | 37 |
| 5 | 221 |
| 6 | -2549 |
| 7 | -21041 |
| 8 | 342665 |
| 9 | 3604537 |
| 10 | -75816809 |
| 11 | -970017949 |
| 12 | 25012223149 |
| 13 | 377031935125 |
| 14 | -11513789879773 |
| 15 | -199833956857289 |
| 16 | 7052339905578001 |
| 17 | 138505710577529969 |
| 18 | -5546345926322582225 |
| 19 | -121599560980889072693 |
| 20 | 5447342134797972438581 |