A151584 Number of permutations of 2 indistinguishable copies of 1..n arranged in a circle with exactly 3 adjacent element pairs in decreasing order.
0, 36, 1088, 14220, 134928, 1093316, 8120064, 57280284, 391301840
Offset: 2
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.