A151657 Number of permutations of 7 indistinguishable copies of 1..n with exactly 3 adjacent element pairs in decreasing order.
0, 1225, 818300, 160310458, 22727054364, 2892619063243, 354402440786800, 42837393111682484, 5153280785356119360, 618914057659003904189, 74290570601695876667092, 8915697686087571194412590, 1069916360274028756641650036, 128391238501628502906890984271
Offset: 1
Keywords
Links
- Andrew Howroyd, Table of n, a(n) for n = 1..200
Programs
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PARI
a(n) = {120^n - (7*n + 1)*36^n + binomial(7*n+1, 2)*8^n - binomial(7*n+1, 3)} \\ Andrew Howroyd, May 07 2020
Formula
a(n) = 120^n - (7*n + 1)*36^n + binomial(7*n+1, 2)*8^n - binomial(7*n+1, 3). - Andrew Howroyd, May 07 2020
Extensions
Terms a(7) and beyond from Andrew Howroyd, May 07 2020