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 | 0 |
| 1 | 1 |
| 2 | -1 |
| 3 | 1 |
| 4 | -13 |
| 5 | 61 |
| 6 | -601 |
| 7 | 5881 |
| 8 | -73333 |
| 9 | 1021861 |
| 10 | -16334401 |
| 11 | 290146561 |
| 12 | -5707536253 |
| 13 | 122821558861 |
| 14 | -2873553719401 |
| 15 | 72586328036041 |
| 16 | -1969306486088773 |
| 17 | 57106504958139061 |
| 18 | -1762735601974347601 |
| 19 | 57705363524117482321 |
| 20 | -1996916624448159410893 |