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 | 5 |
| 4 | -18 |
| 5 | 109 |
| 6 | -720 |
| 7 | 5977 |
| 8 | -56336 |
| 9 | 612729 |
| 10 | -7453440 |
| 11 | 100954061 |
| 12 | -1502172672 |
| 13 | 24395453861 |
| 14 | -429076910080 |
| 15 | 8128143367905 |
| 16 | -164961704478720 |
| 17 | 3571195811862385 |
| 18 | -82142328351817728 |
| 19 | 2000535014776893973 |