%I A081555
%S A081555 3,7,35,199,1155,6727,39203,228487,1331715,7761799,45239075,263672647,
%T A081555 1536796803,8957108167,52205852195,304278004999,1773462177795,
%U A081555 10336495061767,60245508192803,351136554095047,2046573816377475
%N A081555 a(n)=6a(n-1)-a(n-2)-4, a(0)=3, a(1)=7.
%C A081555 a(n)=A003499(n)+1. a(2n)+1=A003499(n)^2. 2(a(2n+1)+1) is a perfect square.
%H A081555 <a href="Sindx_Tu.html#2wis">Index entries for two-way infinite sequences</
               a>
%F A081555 a(n) = (3+2sqrt(2))^n + (3-2sqrt(2))^n + 1
%F A081555 G.f.: (3-14x+7x^2)/((1-x)(1-6x+x^2))
%t A081555 r[n_] := r[n] = 6*r[n - 1] - r[n - 2] - 4; r[0] = 3; r[1] = 7; Table[r[n], 
               {n, 0, 25}]
%o A081555 (PARI) a(n)=1+2*real((3+quadgen(32))^n)
%o A081555 (PARI) a(n)=1+2*subst(poltchebi(abs(n)),x,3)
%o A081555 (PARI) a(n)=if(n<0,a(-n),1+polsym(1-6*x+x^2,n)[n+1])
%Y A081555 a(n)=A051927(2n).
%Y A081555 Sequence in context: A006099 A053530 A132102 this_sequence A027624 A063042 
               A108505
%Y A081555 Adjacent sequences: A081552 A081553 A081554 this_sequence A081556 A081557 
               A081558
%K A081555 easy,nonn
%O A081555 0,1
%A A081555 Mario Catalani (mario.catalani(AT)unito.it), Mar 24 2003