0,2

a(n) = (Pi/4)*n + O(sqrt(n)).

Table of n, a(n) for n=0..60.

V. Shevelev, Binary additive problems: theorems of Landau and Hardy-Littlewood type, arXiv:0902.1046 [math.NT], 2009-2012.

a(n) = sum_{k=1..r(n)} r(2n-k^2+k)-C(r(n),2) where r(n) = A000194(n+1).

terms = 61; QP = QPochhammer;

s = QP[q^2]^4/QP[q]^2 + O[q]^terms;

Ceiling[CoefficientList[s, q]/2] // Accumulate (* Jean-François Alcover, Feb 17 2019 *)

Cf. A052343, A000194.

Sequence in context: A088468 A049448 A130044 * A082081 A008475 A222416

Adjacent sequences: A156226 A156227 A156228 * A156230 A156231 A156232

nonn

Vladimir Shevelev, Feb 06 2009

approved