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 | -2 |
| 4 | -8 |
| 5 | -36 |
| 6 | -200 |
| 7 | -1328 |
| 8 | -10224 |
| 9 | -89360 |
| 10 | -873152 |
| 11 | -9425952 |
| 12 | -111365120 |
| 13 | -1428894656 |
| 14 | -19781794944 |
| 15 | -293869134848 |
| 16 | -4662342567680 |
| 17 | -78672085380864 |
| 18 | -1406772851720192 |
| 19 | -26571340011921920 |
| 20 | -528613254534998016 |