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a(n) = floor(n*(n-1)/16).
1

%I #23 Sep 08 2022 08:44:37

%S 0,0,0,0,0,1,1,2,3,4,5,6,8,9,11,13,15,17,19,21,23,26,28,31,34,37,40,

%T 43,47,50,54,58,62,66,70,74,78,83,87,92,97,102,107,112,118,123,129,

%U 135,141,147,153,159,165,172,178,185,192,199,206,213,221,228,236,244,252,260

%N a(n) = floor(n*(n-1)/16).

%H Matthew House, <a href="/A011869/b011869.txt">Table of n, a(n) for n = 0..10000</a>

%H <a href="/index/Rec#order_17">Index entries for linear recurrences with constant coefficients</a>, signature (3,-4,4,-4,4,-4,4,-4,4,-4,4,-4,4,-4,4,-3,1).

%F G.f.: -((x^5 (1-x+x^2) (1-x+x^2-x^3+x^4-x^5+x^6))/((-1+x)^3 (1+x^2) (1+x^4) (1+x^8)))

%t Table[Floor[(n(n-1))/16],{n,0,70}] (* or *) LinearRecurrence[{3,-4,4,-4,4,-4,4,-4,4,-4,4,-4,4,-4,4,-3,1},{0,0,0,0,0,1,1,2,3,4,5,6,8,9,11,13,15},70] (* _Harvey P. Dale_, May 23 2019 *)

%o (Magma) [(n*(n-1) div 16) : n in [0..70]]; // _Vincenzo Librandi_, May 26 2019

%Y Cf. A011861.

%K nonn

%O 0,8

%A _N. J. A. Sloane_.