A211371 - OEIS

%I #15 Sep 18 2013 06:24:16

%S 0,1,1,3,7,29,131,585,3083,17089,97987,607977,3926731,26344001,

%T 185908739,1358432937,10279616891,80819893393,655374770131,

%U 5482528852761,47329769940331,420061520283617,3832533793409027,35926633641149865,345280194806563931

%N The number of indecomposable n-permutations that have only cycles of length 3 or less.

%F G.f.: 1-1/A(x) where A(x) is the o.g.f. for A057693.

%e a(4) = 7 because we have: 2431, 3241, 3412, 4132, 4213, 4231, 4321.

%t nn = 20; a = x + x^2/2 + x^3/3; b = Total[Range[0, nn]! CoefficientList[Series[Exp[a], {x, 0, nn}], x]* x^Range[0, nn]]; CoefficientList[Series[1 - 1/b, {x, 0, nn}], x]

%Y Cf. A057693, A003319, A140456.

%K nonn

%O 0,4

%A _Geoffrey Critzer_, May 11 2012