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 | 15 |
| 5 | 87 |
| 6 | -609 |
| 7 | -8337 |
| 8 | 125055 |
| 9 | 2695455 |
| 10 | -83559105 |
| 11 | -4212669825 |
| 12 | 265398198975 |
| 13 | 22347926076735 |
| 14 | -2838186611745345 |
| 15 | -560679228377509185 |
| 16 | 142973203236264842175 |
| 17 | 47858338570309251530175 |
| 18 | -24455611009428027531919425 |
| 19 | -19225279650279123532147010625 |