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a(n) = 6*n - floor(3*n*sqrt(3)).
1

%I #19 Sep 08 2022 08:45:59

%S 0,1,2,3,4,5,5,6,7,8,9,9,10,11,12,13,13,14,15,16,17,17,18,19,20,21,21,

%T 22,23,24,25,25,26,27,28,29,29,30,31,32,33,33,34,35,36,37,37,38,39,40,

%U 41,41,42,43,44,45,46,46,47,48,49,50,50,51,52,53,54,54,55,56

%N a(n) = 6*n - floor(3*n*sqrt(3)).

%H Vincenzo Librandi, <a href="/A195181/b195181.txt">Table of n, a(n) for n = 0..10000</a>

%F a(n) = A195120(3*n). - _R. J. Mathar_, Sep 11 2011

%p A195181:=n->6*n-floor(3*n*sqrt(3)): seq(A195181(n), n=0..150); # _Wesley Ivan Hurt_, Jan 21 2017

%t Table[6*n - Floor[3*n*Sqrt[3]], {n,0,50}] (* _G. C. Greubel_, Nov 01 2017 *)

%o (Magma) [6*n-Floor(3*n*Sqrt(3)): n in [0..70]]; // _Vincenzo Librandi_, Sep 12 2011

%o (PARI) for(n=0,50, print1(6*n - floor(3*n*sqrt(3)), ", ")) \\ _G. C. Greubel_, Nov 01 2017

%Y Cf. A195120.

%K nonn,easy

%O 0,3

%A _Clark Kimberling_, Sep 10 2011