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0, 4, 32, 192, 1024, 5120, 24576, 114688, 524288, 2359296, 10485760, 46137344, 201326592, 872415232, 3758096384, 16106127360, 68719476736, 292057776128, 1236950581248, 5222680231936, 21990232555520
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OFFSET
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0,2
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COMMENTS
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All numbers of the form n*4^n+(4^n-1)/3 have the property that they are sums of two squares and also their indices are the sum of two squares. This follows from the identity n*4^n+(4^n-1)/3=4*(4*(..4*(4*n+1)+1)+1)+1..)+1. - Artur Jasinski, Nov 12 2007
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LINKS
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FORMULA
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G.f.: 4*x/(1-4*x)^2.
E.g.f.: 4*x*exp(4*x).
Sum_{n>=1} 1/a(n) = log(4/3) = A083679.
Sum_{n>=1} (-1)^(n+1)/a(n) = log(5/4). (End)
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MATHEMATICA
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Table[n 4^n, {n, 0, 20}] (* or *) LinearRecurrence[{8, -16}, {0, 4}, 30] (* Harvey P. Dale, Apr 22 2018 *)
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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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STATUS
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approved
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