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 | -3 |
| 4 | 4 |
| 5 | -30 |
| 6 | 186 |
| 7 | -630 |
| 8 | 11600 |
| 9 | -26712 |
| 10 | 1005480 |
| 11 | -2581920 |
| 12 | 117196872 |
| 13 | -485308824 |
| 14 | 17734457664 |
| 15 | -131070696120 |
| 16 | 3387342915840 |
| 17 | -43890398953920 |
| 18 | 801577841697216 |
| 19 | -17363169328243392 |
| 20 | 233460174245351040 |
| 21 | -7968629225100337920 |
| 22 | 84363134551361043840 |