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 | 0 |
| 3 | 15 |
| 4 | -136 |
| 5 | 885 |
| 6 | -4896 |
| 7 | 43085 |
| 8 | -787200 |
| 9 | 7775271 |
| 10 | 326355200 |
| 11 | -22138191801 |
| 12 | 781498160640 |
| 13 | -18924340012435 |
| 14 | 239123351330304 |
| 15 | 5915023788331125 |
| 16 | -568462201562300416 |
| 17 | 25327272129182225295 |
| 18 | -795994018378027868160 |
| 19 | 15538852668590468027711 |