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 | 0 |
| 4 | 0 |
| 5 | 0 |
| 6 | 120 |
| 7 | -120 |
| 8 | -720 |
| 9 | -5040 |
| 10 | -40320 |
| 11 | -362880 |
| 12 | 3024000 |
| 13 | 21859200 |
| 14 | 151113600 |
| 15 | 753667200 |
| 16 | -3978374400 |
| 17 | -249882796800 |
| 18 | -1752623308800 |
| 19 | -7319841177600 |
| 20 | 79100731699200 |
| 21 | 2905096654540800 |
| 22 | 48387220210944000 |
| 23 | 226481995918080000 |
| 24 | -2094278695939584000 |
| 25 | -85503113536135680000 |