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%I #6 May 07 2020 22:33:16
%S 0,1225,818300,160310458,22727054364,2892619063243,354402440786800,
%T 42837393111682484,5153280785356119360,618914057659003904189,
%U 74290570601695876667092,8915697686087571194412590,1069916360274028756641650036,128391238501628502906890984271
%N Number of permutations of 7 indistinguishable copies of 1..n with exactly 3 adjacent element pairs in decreasing order.
%H Andrew Howroyd, <a href="/A151657/b151657.txt">Table of n, a(n) for n = 1..200</a>
%F 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
%o (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
%Y Cf. A151625, A151656.
%K nonn
%O 1,2
%A _R. H. Hardin_, May 29 2009
%E Terms a(7) and beyond from _Andrew Howroyd_, May 07 2020