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 | 2 |
| 2 | 5 |
| 3 | -1 |
| 4 | -116 |
| 5 | 984 |
| 6 | 16400 |
| 7 | -788418 |
| 8 | 5474016 |
| 9 | 941115360 |
| 10 | -51647682648 |
| 11 | -264087895512 |
| 12 | 244846563852864 |
| 13 | -16953959408998080 |
| 14 | -436871956049596800 |
| 15 | 219647419965976413744 |
| 16 | -20283048895473275917824 |
| 17 | -877465277974899660349440 |
| 18 | 545297904370739513319183360 |