Search: id:A054974
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%I A054974
%S A054974 1,2,6,9,17,23,36,46,65,80,106,127,161,189,232,268,321,366,430,485,561,
%T A054974 627,716,794,897,988,1106,1211,1345,1465,1616,1752,1921,2074,2262,2433,
%U A054974 2641,2831,3060,3270,3521,3752,4026,4279,4577,4853,5176,5476,5825,6150
%N A054974 Number of nonnegative integer 2 X 2 matrices with no zero rows or columns 
               and with sum of elements equal to n, up to row and column permutation.
%F A054974 G.f.: -x^2*(x^3-x^2-1)/((x^2-1)^2*(x-1)^2).
%e A054974 There are 9 nonnegative integer 2 X 2 matrices with no zero rows or columns 
               and with sum of elements equal to 5, up to row and column permutation:
%e A054974 [0 1] [0 1] [0 1] [0 1] [0 2] [0 2] [0 2] [0 3] [1 1]
%e A054974 [1 3] [2 2] [3 1] [4 0] [1 2] [2 1] [3 0] [1 1] [1 2].
%p A054974 gf := -x^2*(x^3-x^2-1)/((x^2-1)^2*(x-1)^2): s := series(gf, x, 101): 
               for i from 2 to 100 do printf(`%d,`,coeff(s,x,i)) od:
%Y A054974 Cf. A053307.
%Y A054974 Sequence in context: A103139 A049622 A043548 this_sequence A072481 A032471 
               A156222
%Y A054974 Adjacent sequences: A054971 A054972 A054973 this_sequence A054975 A054976 
               A054977
%K A054974 easy,nonn
%O A054974 2,2
%A A054974 Vladeta Jovovic (vladeta(AT)eunet.rs), May 28 2000
%E A054974 More terms from James A. Sellers (sellersj(AT)math.psu.edu), May 29 2000

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