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 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | -3 |
| 4 | 13 |
| 5 | -70 |
| 6 | 447 |
| 7 | -3297 |
| 8 | 27576 |
| 9 | -257904 |
| 10 | 2667240 |
| 11 | -30226680 |
| 12 | 372517920 |
| 13 | -4960668960 |
| 14 | 70986162240 |
| 15 | -1086347505600 |
| 16 | 17705365171200 |
| 17 | -306178316236800 |
| 18 | 5599477712102400 |
| 19 | -107980208561433600 |
| 20 | 2189837602616832000 |