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A011881 a(n) = floor(n*(n-1)/28). 0

%I #14 Sep 28 2022 03:44:02

%S 0,0,0,0,0,0,1,1,2,2,3,3,4,5,6,7,8,9,10,12,13,15,16,18,19,21,23,25,27,

%T 29,31,33,35,37,40,42,45,47,50,52,55,58,61,64,67,70,73,77,80,84,87,91,

%U 94,98,102,106,110,114,118

%N a(n) = floor(n*(n-1)/28).

%H <a href="/index/Rec#order_23">Index entries for linear recurrences with constant coefficients</a>, signature (2, -1, 0, 0, 0, 0, 1, -2, 1, 0, 0, 0, 0, -1, 2, -1, 0, 0, 0, 0, 1, -2, 1).

%F G.f.: (x^6 (-1-(-1+x) x (1+(-1+x) x) (1+x^2) (1+x+x^2) (1-x^2+x^4)))/(-1+x (2+x (-1+(-1+x)^2 x^5 (1-x^7+x^14)))) _Peter J. C. Moses_, Jun 01 2014

%F a(n)= +2*a(n-1) -a(n-2) +a(n-7) -2*a(n-8) +a(n-9) -a(n-14) +2*a(n-15) -a(n-16) +a(n-21) -2*a(n-22) +a(n-23). - _R. J. Mathar_, Aug 11 2021

%t Table[Floor[(n(n-1))/28],{n,0,60}] (* or *) LinearRecurrence[{2,-1,0,0,0,0,1,-2,1,0,0,0,0,-1,2,-1,0,0,0,0,1,-2,1},{0,0,0,0,0,0,1,1,2,2,3,3,4,5,6,7,8,9,10,12,13,15,16},60] (* _Harvey P. Dale_, Apr 18 2022 *)

%K nonn,easy

%O 0,9

%A _N. J. A. Sloane_.

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Last modified March 28 22:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)