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A161320 Floor of Sum_{k=1..n} Sum_{m=1..k} (2*cosh(Pi*m/(2*k)) - 1). 0

%I

%S 4,9,17,26,37,51,66,83,102,122,145,170,197,225,256,288,323,359,397,

%T 437,479,523,569,617,667,718,772,828,885,945,1006,1069,1135,1202,1271,

%U 1342,1415,1490,1566,1645,1726,1808,1893,1979,2068,2158,2250,2344,2440,2539

%N Floor of Sum_{k=1..n} Sum_{m=1..k} (2*cosh(Pi*m/(2*k)) - 1).

%C Pi in the definition is A000796.

%C a(n) appears to oscillate near (n+1)^2.

%F a(n) = floor(2*Sum_{k=1..n} Sum_{m=1..k} cosh(Pi*m/(2*k)) - A000217(n)).

%t Floor[N[Table[Sum[(2*Cos[Pi*I*i/(2j)]-1),{j,1,k},{i,1,j}],{k,1,20}]]]

%K nonn

%O 1,1

%A _Daniel Tisdale_, Jun 06 2009

%E Variables redefined, sequence extended by _R. J. Mathar_, Aug 30 2010

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Last modified September 26 09:15 EDT 2021. Contains 347664 sequences. (Running on oeis4.)