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a(n) = floor(n/4)*ceiling(n/4).
0

%I #18 Jun 08 2017 16:44:46

%S 0,0,0,0,1,2,2,2,4,6,6,6,9,12,12,12,16,20,20,20,25,30,30,30,36,42,42,

%T 42,49,56,56,56,64,72,72,72,81,90,90,90,100,110,110,110,121,132,132,

%U 132,144,156,156,156,169,182,182

%N a(n) = floor(n/4)*ceiling(n/4).

%H <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (2,-2,2,0,-2,2,-2,1).

%F G.f.: x^4/((1-x)^3*(1+x)*(1+x^2)^2). - _R. J. Mathar_, Mar 11 2012

%F a(n) = floor(n/4)*floor((n+3)/4). - _Bruno Berselli_, Jun 08 2017

%t f[n_]:=Module[{c=n/4},Floor[c]Ceiling[c]]; f/@Range[0,70] (* _Harvey P. Dale_, Apr 23 2011 *)

%Y Cf. A002265.

%K nonn,easy

%O 0,6

%A _N. J. A. Sloane_