A151585 Number of permutations of 2 indistinguishable copies of 1..n arranged in a circle with exactly 4 adjacent element pairs in decreasing order.
0, 3, 976, 44275, 1046556, 18098871, 262962368, 3438697635, 42050013500
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.