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A229135
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n * (2 + 2^(2*n - 1)).
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2
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0, 4, 20, 102, 520, 2570, 12300, 57358, 262160, 1179666, 5242900, 23068694, 100663320, 436207642, 1879048220, 8053063710, 34359738400, 146028888098, 618475290660, 2611340116006, 10995116277800, 46179488366634, 193514046488620, 809240558043182, 3377699720527920
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OFFSET
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0,2
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COMMENTS
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a(n) mod 9 is periodic: repeat 0, 4, 2, 3, 7, 5, 6, 1, 8.
b(n) = a(n) - n = 0, 3, 18, 99, 516, 2565, 12294,... = A215149(2n)/2.
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LINKS
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FORMULA
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G.f.: (34*x^3 - 20*x^2 + 4*x)/((1-x)^2*(1-4*x)^2). - Ralf Stephan, Sep 20 2013
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EXAMPLE
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a(0)=0*(2+1/2)=0, a(1)=1*(2+2)=4, a(2)=2*(2+8)=20, a(3)=3*(2+32)=102, a(4)=4*(2+128)=520, a(5)=5*(2+512)=2570.
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MATHEMATICA
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PROG
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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Better definition by Michel Marcus.
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STATUS
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approved
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