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 | -2 |
| 2 | 0 |
| 3 | 40 |
| 4 | 0 |
| 5 | -4032 |
| 6 | 0 |
| 7 | 933504 |
| 8 | 0 |
| 9 | -385848320 |
| 10 | 0 |
| 11 | 249576198144 |
| 12 | 0 |
| 13 | -232643283353600 |
| 14 | 0 |
| 15 | 295306112919306240 |
| 16 | 0 |
| 17 | -489743069731226910720 |
| 18 | 0 |
| 19 | 1028154317960939805081600 |
| 20 | 0 |
| 21 | -2665182817368374114506506240 |
| 22 | 0 |
| 23 | 8360422228704533182913131315200 |