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%I #33 Dec 11 2016 11:43:29
%S 0,0,0,1,6,41,274,2040,16346,143571,1365354,14056287,155638724,
%T 1847352720,23400880036,315270938501,4502081195166,67941159822229,
%U 1080528172834710,18065046986905320,316769071197428286,5813469963339136855,111449225620923739458
%N Number of permutations of [n] having exactly one doubledescent.
%H Alois P. Heinz, <a href="/A274997/b274997.txt">Table of n, a(n) for n = 0..463</a>
%F a(n) ~ c * 3^(3*n/2) * n^(n+3/2) / (exp(n) * 2^n * Pi^n), where c = 0.827206526063705458546024... . - _Vaclav Kotesovec_, Dec 11 2016
%Y Column k=1 of A162975.
%K nonn
%O 0,5
%A _Alois P. Heinz_, Nov 29 2016