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A181972 Number of integer pairs (x,y) such that 0 and x*y<=floor(n/2).

%I A181972 #9 Apr 07 2012 13:47:29
%S A181972 0,0,0,1,1,2,2,3,3,4,4,6,6,7,7,9,9,10,10,12,12,13,13,16,16,17,17,19,
%T A181972 19,21,21,23,23,24,24,27,27,28,28,31,31,33,33,35,35,36,36,40,40,41,41,
%U A181972 43,43,45,45,48,48,49,49,53,53,54,54,57,57,59,59,61,61,63,63,67
%N A181972 Number of integer pairs (x,y) such that 0<x<y<=n and x*y<=floor(n/2).
%C A181972 For a guide to related sequences, see A211266.
%t A181972 a = 1; b = n; z1 = 120;
%t A181972 t[n_] := t[n] = Flatten[Table[x*y, {x, a, b - 1},
%t A181972  {y, x + 1, b}]]
%t A181972 c[n_, k_] := c[n, k] = Count[t[n], k]
%t A181972 Table[c[n, n], {n, 1, z1}]           (* A056924 *)
%t A181972 Table[c[n, n + 1], {n, 1, z1}]       (* A211159 *)
%t A181972 Table[c[n, 2*n], {n, 1, z1}]         (* A211261 *)
%t A181972 Table[c[n, 3*n], {n, 1, z1}]         (* A211262 *)
%t A181972 Table[c[n, Floor[n/2]], {n, 1, z1}]  (* A211263 *)
%t A181972 Print
%t A181972 c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, a, m}]
%t A181972 Table[c1[n, n], {n, 1, z1}]          (* A211264 *)
%t A181972 Table[c1[n, n + 1], {n, 1, z1}]      (* A211265 *)
%t A181972 Table[c1[n, 2*n], {n, 1, z1}]        (* A211266 *)
%t A181972 Table[c1[n, 3*n], {n, 1, z1}]        (* A211267 *)
%t A181972 Table[c1[n, Floor[n/2]], {n, 1, z1}] (* A181972 *)
%Y A181972 Cf. A211266.
%K A181972 nonn
%O A181972 1,6
%A A181972 _Clark Kimberling_, Apr 06 2012