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 | -2 |
| 4 | -11 |
| 5 | 24 |
| 6 | 349 |
| 7 | -720 |
| 8 | -22455 |
| 9 | 40320 |
| 10 | 2465241 |
| 11 | -3628800 |
| 12 | -416217603 |
| 13 | 479001600 |
| 14 | 100729124469 |
| 15 | -87178291200 |
| 16 | -33198564667887 |
| 17 | 20922789888000 |
| 18 | 14328891118054449 |
| 19 | -6402373705728000 |
| 20 | -7852649782447649403 |