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A047215
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Numbers that are congruent to {0, 2} mod 5.
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33
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0, 2, 5, 7, 10, 12, 15, 17, 20, 22, 25, 27, 30, 32, 35, 37, 40, 42, 45, 47, 50, 52, 55, 57, 60, 62, 65, 67, 70, 72, 75, 77, 80, 82, 85, 87, 90, 92, 95, 97, 100, 102, 105, 107, 110, 112, 115, 117, 120, 122, 125, 127, 130, 132, 135, 137, 140, 142, 145, 147, 150, 152, 155, 157
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OFFSET
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0,2
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COMMENTS
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Number of partitions of 5n into exactly 2 parts. - Colin Barker, Mar 23 2015
Numbers k such that k^2/5 + k*(k + 1)/5 = k*(2*k + 1)/5 is a nonnegative integer. - Bruno Berselli, Feb 14 2017
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LINKS
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Table of n, a(n) for n=0..63.
Index entries for linear recurrences with constant coefficients, signature (1,1,-1).
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FORMULA
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a(n) = floor(5*n/2).
From R. J. Mathar, Sep 23 2008: (Start)
G.f.: x*(2 + 3*x)/((1 + x)*(1 - x)^2).
a(n) = 5*n/2 +((-1)^n-1)/4.
a(n+1)-a(n) = A010693(n+1). (End)
a(n) = 5*n - a(n-1) - 8 with a(1)=0. - Vincenzo Librandi, Aug 05 2010
a(n+1) = Sum_{k>=0} A030308(n,k)*A084215(k+1). - Philippe Deléham, Oct 17 2011
a(n) = 2*n + floor(n/2). - Arkadiusz Wesolowski, Sep 19 2012
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MATHEMATICA
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Table[Floor[5 n/2], {n, 0, 100}] (* or *) LinearRecurrence[{1, 1, -1}, {0, 2, 5}, 101] (* Vladimir Joseph Stephan Orlovsky, Jan 28 2012 *)
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PROG
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(PARI) a(n)=5*n\2 \\ Charles R Greathouse IV, Oct 17 2011
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CROSSREFS
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Different from A038126.
Sequence in context: A022849 A075328 A038126 * A330067 A059536 A030193
Adjacent sequences: A047212 A047213 A047214 * A047216 A047217 A047218
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane
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STATUS
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approved
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