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A006457
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Number of elements in Z[ i ] whose 'smallest algorithm' is <= n.
(Formerly M3873)
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3
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1, 5, 17, 49, 125, 297, 669, 1457, 3093, 6457, 13309, 27201, 55237, 111689, 225101, 452689, 908885, 1822809, 3652701, 7315553, 14645349, 29311081, 58650733, 117342321, 234741877, 469565561, 939245693, 1878655105, 3757539461, 7515406473, 15031271565
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OFFSET
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0,2
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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FORMULA
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a(n+5) - 4*a(n+4) + 3*a(n+3) + 6*a(n+2) - 10*a(n+1) + 4*a(n) = 0.
a(2k) = 14*4^k - 34*2^k + 8*k + 21.
a(2k+1) = 28*4^k - 48*2^k + 8*k + 25.
For n >= 3, a(n) == 5 + 4*n (mod 8). (End)
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MAPLE
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A006457:=(1+z+2*z^3)/(2*z-1)/(2*z^2-1)/(z-1)^2; # conjectured by Simon Plouffe in his 1992 dissertation
seq(op([14*4^k-34*2^k+8*k+21, 28*4^k-48*2^k+8*k+25]), k=0..50); # Robert Israel, Aug 02 2016
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MATHEMATICA
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CoefficientList[Series[(1+x+2x^3)/(2x-1)/(2x^2-1)/(x-1)^2, {x, 0, 30}], x] (* or *) LinearRecurrence[{4, -3, -6, 10, -4}, {1, 5, 17, 49, 125}, 30] (* Harvey P. Dale, Jun 22 2011 *)
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CROSSREFS
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KEYWORD
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nonn,easy,nice
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AUTHOR
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H. W. Lenstra, Jr.
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STATUS
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approved
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