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 A047215 Numbers that are congruent to {0, 2} mod 5. 33
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS 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 LINKS Index entries for linear recurrences with constant coefficients, signature (1,1,-1). FORMULA 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 MATHEMATICA Table[Floor[5 n/2], {n, 0, 100}] (* or *) LinearRecurrence[{1, 1, -1}, {0, 2, 5}, 101] (* Vladimir Joseph Stephan Orlovsky, Jan 28 2012 *) PROG (PARI) a(n)=5*n\2 \\ Charles R Greathouse IV, Oct 17 2011 CROSSREFS Different from A038126. Sequence in context: A022849 A075328 A038126 * A330067 A059536 A030193 Adjacent sequences:  A047212 A047213 A047214 * A047216 A047217 A047218 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified April 17 08:24 EDT 2021. Contains 343064 sequences. (Running on oeis4.)