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A051253
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Weights of rotation-symmetric functions in n variables.
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4
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1, 4, 6, 18, 36, 80, 172, 360, 760, 1576, 3264, 6720, 13776, 28160, 57376, 116640, 236608, 479104, 968640, 1955712, 3944064, 7945856, 15993856, 32168448, 64656640, 129879040, 260759040, 523289088, 1049711616, 2104967168, 4219743232, 8456841216, 16944388096
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OFFSET
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3,2
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LINKS
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FORMULA
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a(n+3) = 2*a(n+1)+2*a(n)+2^n.
G.f.: -(8*x^6)/(1-2*x)+x^3+*x^4+4*x^5)/(-1+2*x^2+2*x^3).
a(3)=1, a(4)=4, a(5)=6, a(6)=18, a(n) = 2*a(n-1)+2*a(n-2)-2*a(n-3)-4*a(n-4). - Harvey P. Dale, Mar 15 2015
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EXAMPLE
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a(3)=1 since the rotation-symmetric function x_1*x_2*x_3 has Hamming weight 1.
a(4)=4 since the rotation-symmetric function x_1*x_2*x_3+x_2*x_3*x_4+x_3*x_4*x_1+x_4*x_1*x_2 has Hamming weight 4.
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MAPLE
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t1:=(8*x^6/(1-2*x) + x^3 + 4*x^4 + 4*x^5)/(1-2*x^2-2*x^3);
t2:=series(t1, x, 40);
seriestolist(%);
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MATHEMATICA
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LinearRecurrence[{2, 2, -2, -4}, {1, 4, 6, 18}, 40] (* Harvey P. Dale, May 05 2011 *)
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PROG
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(PARI) a(n)=([0, 1, 0, 0; 0, 0, 1, 0; 0, 0, 0, 1; -4, -2, 2, 2]^(n-3)*[1; 4; 6; 18])[1, 1] \\ Charles R Greathouse IV, Feb 19 2017
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CROSSREFS
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KEYWORD
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nice,easy,nonn
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AUTHOR
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Pantelimon Stanica (stanpan(AT)sciences.aum.edu)
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EXTENSIONS
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STATUS
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approved
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