%I A051927
%S A051927 3,1,7,13,35,81,199,477,1155,2785,6727,16237,39203,94641,228487,551613,
%T A051927 1331715,3215041,7761799,18738637,45239075,109216785,263672647,
%U A051927 636562077,1536796803,3710155681,8957108167,21624372013,52205852195
%N A051927 Number of independent sets of vertices in graph K_2 X C_n (n > 2).
%F A051927 a(n) = a(n-1) + 3*a(n-2) + a(n-3)
%F A051927 G.f.: (3-2x-3x^2)/((1-2x-x^2)(1+x)). - Michael Somos, Apr 07 2003
%F A051927 Let A=[0, 1, 1;1, 1, 1;1, 1, 0] be the adjacency matrix of a triangle 
               with a loop at a vertex. Then a(n)=trace(A^n). a(n)=(-1)^n+(1-sqrt(2))^n+(1+sqrt(2))^n. 
               - Paul Barry (pbarry(AT)wit.ie), Jul 22 2004
%o A051927 (PARI) a(n)=polcoeff((3-2*x-3*x^2)/(1-2*x-x^2)/(1+x)+x*O(x^n),n)
%Y A051927 Sequence in context: A033465 A096431 A113647 this_sequence A101845 A096643 
               A036575
%Y A051927 Adjacent sequences: A051924 A051925 A051926 this_sequence A051928 A051929 
               A051930
%K A051927 easy,nonn
%O A051927 0,1
%A A051927 Stephen G. Penrice (spenrice(AT)ets.org), Dec 19 1999