%I A006904 M3254
%S A006904 1,1,4,5,14,23,52,97,202,395,800,1589,3190,6367,12748,25481,50978,101939,
               203896,
%T A006904 407773,815566,1631111,3262244,6524465,13048954,26097883,52195792,104391557
%N A006904 a(n) = a(n-1)+2.a(n-2)+(-1)^n.
%D A006904 R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, 
               Reading, MA, 1990, p. 327.
%D A006904 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%F A006904 G.f.: (1+x+x^2 ) / (1-2x)(1+x)^2.
%F A006904 With offset 0: a(n) = 1/9*(7*2^n+(-1)^n*(3*n+2)); if b(1)=1, b(k) = 2*b(k-1)+(-1)^k*k, 
               then for n>4, a(n)=b(n-4). - Benoit Cloitre (benoit7848c(AT)orange.fr), 
               Oct 28 2002
%Y A006904 Sequence in context: A041089 A042321 A050164 this_sequence A007084 A093862 
               A041375
%Y A006904 Adjacent sequences: A006901 A006902 A006903 this_sequence A006905 A006906 
               A006907
%K A006904 nonn,easy
%O A006904 4,3
%A A006904 Simon Plouffe, N. J. A. Sloane (njas(AT)research.att.com).