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 | 120 |
| 6 | 1800 |
| 7 | 16800 |
| 8 | 126000 |
| 9 | 834120 |
| 10 | 8731800 |
| 11 | 229191600 |
| 12 | 6352632000 |
| 13 | 143603580120 |
| 14 | 2736395461800 |
| 15 | 47283190718400 |
| 16 | 860150574738000 |
| 17 | 20236134851478120 |
| 18 | 614854122909391800 |
| 19 | 19930647062659477200 |
| 20 | 615406024970593164000 |
| 21 | 17883373100352330768120 |