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a(n) = 3*n - floor(n*r/3), where r=(1+sqrt(5))/2 (the golden ratio).
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%I #12 Sep 08 2022 08:45:59

%S 0,3,5,8,10,13,15,18,20,23,25,28,30,32,35,37,40,42,45,47,50,52,55,57,

%T 60,62,64,67,69,72,74,77,79,82,84,87,89,92,94,96,99,101,104,106,109,

%U 111,114,116,119,121,124,126,128,131,133,136,138,141,143,146,148

%N a(n) = 3*n - floor(n*r/3), where r=(1+sqrt(5))/2 (the golden ratio).

%H Vincenzo Librandi, <a href="/A195168/b195168.txt">Table of n, a(n) for n = 0..10000</a>

%t With[{c = GoldenRatio},Table[3*n - Floor[c*n/3],{n,0,50}]] (* _G. C. Greubel_, Oct 31 2017 *)

%o (Magma) [3*n-Floor(n*(1+Sqrt(5))/6): n in [0..70]]; // _Vincenzo Librandi_, Sep 11 2011

%o (PARI) for(n=0,50, print1(3*n - floor(n*(1+sqrt(5))/6), ", ")) \\ _G. C. Greubel_, Oct 31 2017

%K nonn

%O 0,2

%A _Clark Kimberling_, Sep 10 2011