A151577 Number of permutations of 1..n arranged in a circle with exactly 4 adjacent element pairs in decreasing order.
0, 5, 156, 2114, 19328, 140571, 882340, 5007112, 26441856, 132439905, 637468300, 2976161790, 13569454592, 60725449335, 267757190100, 1166662948900, 5034645823680, 21556696454685, 91704869986620, 388044105102650, 1634678955350400, 6860481786528275, 28700914012807556
Offset: 4
Keywords
Links
- Andrew Howroyd, Table of n, a(n) for n = 4..500
Programs
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PARI
a(n) = {n*(4^(n-1) - n*3^(n-1) + binomial(n,2)*2^(n-1) - binomial(n,3))} \\ Andrew Howroyd, May 05 2020
Formula
From Andrew Howroyd, May 05 2020: (Start)
a(n) = n*A000498(n-1).
a(n) = n*(4^(n-1) - n*3^(n-1) + binomial(n,2)*2^(n-1) - binomial(n,3)). (End)
Extensions
Terms a(17) and beyond from Andrew Howroyd, May 05 2020