A151588 Number of permutations of 2 indistinguishable copies of 1..n arranged in a circle with exactly 7 adjacent element pairs in decreasing order.
0, 760, 911520, 222334560, 25996425216, 1996732745784, 117482611237280
Offset: 4
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.