cp's OEIS Frontend

A242536 Number of n-length words on {1,2,3,4} such that the maximal runs of identical odd integers are of odd length and the maximal runs of identical even integers are of even length.

%I A242536 #15 Jun 13 2015 00:55:02
%S A242536 1,2,4,12,26,66,160,386,946,2292,5582,13578,33016,80330,195370,475236,
%T A242536 1155974,2811762,6839416,16636178,40466002,98429844,239421374,
%U A242536 582370554,1416562360,3445657082,8381242522,20386597380,49588514390,120619477410,293395730296
%N A242536 Number of n-length words on {1,2,3,4} such that the maximal runs of identical odd integers are of odd length and the maximal runs of identical even integers are of even length.
%H A242536 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1,3,2,-2)
%F A242536 G.f.: (1 + x - x^2)/(1 - x -3*x^2 - 2*x^3 + 2*x^4).
%F A242536 a(n) = a(n-1) +3*a(n-2) +2*a(n-3) -2*a(n-4). - _Fung Lam_, May 18 2014
%e A242536 a(3)=12 because we have: 111, 122, 131, 144, 221, 223, 313, 322, 333, 344, 441, 443.
%t A242536 n=4;nn=30;CoefficientList[Series[1/(1-Sum[v[i]/(1+v[i]),{i,1,n}])/.Join[Table[v[i]->z/(1-z^2),{i,1,n,2}],Table[v[i]->z^2/(1-z^2),{i,2,n,2}]],{z,0,nn}],z]
%Y A242536 Cf. A062200, A242510, A242537.
%K A242536 nonn,easy
%O A242536 0,2
%A A242536 _Geoffrey Critzer_, May 17 2014