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 | 12 |
| 4 | 0 |
| 5 | 120 |
| 6 | 2160 |
| 7 | 1680 |
| 8 | 120960 |
| 9 | 1481760 |
| 10 | 6350400 |
| 11 | 240166080 |
| 12 | 2754259200 |
| 13 | 31152401280 |
| 14 | 894303970560 |
| 15 | 11769588230400 |
| 16 | 228232766361600 |
| 17 | 5845147711603200 |
| 18 | 98290727395660800 |
| 19 | 2502848611354291200 |
| 20 | 63417766359467520000 |
| 21 | 1376904298716724377600 |