OFFSET
1,1
COMMENTS
Pi in the definition is A000796.
a(n) appears to oscillate near (n+1)^2.
FORMULA
a(n) = floor(2*Sum_{k=1..n} Sum_{m=1..k} cosh(Pi*m/(2*k)) - A000217(n)).
MATHEMATICA
Floor[N[Table[Sum[(2*Cos[Pi*I*i/(2j)]-1), {j, 1, k}, {i, 1, j}], {k, 1, 20}]]]
CROSSREFS
KEYWORD
nonn
AUTHOR
Daniel Tisdale, Jun 06 2009
EXTENSIONS
Variables redefined, sequence extended by R. J. Mathar, Aug 30 2010
STATUS
approved