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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 5 |
| 6 | -15 |
| 7 | 70 |
| 8 | -420 |
| 9 | 3024 |
| 10 | -22050 |
| 11 | 202950 |
| 12 | -2113650 |
| 13 | 24324300 |
| 14 | -305645340 |
| 15 | 4174483950 |
| 16 | -61253992800 |
| 17 | 961049212200 |
| 18 | -16054949350440 |
| 19 | 284505099278400 |
| 20 | -5329752594075000 |
| 21 | 105239780964864000 |
| 22 | -2184466455408699000 |
| 23 | 47550052231211237400 |