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A181972 Number of integer pairs (x,y) such that 0<x<y<=n and x*y<=floor(n/2). 9
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, 19, 21, 21, 23, 23, 24, 24, 27, 27, 28, 28, 31, 31, 33, 33, 35, 35, 36, 36, 40, 40, 41, 41, 43, 43, 45, 45, 48, 48, 49, 49, 53, 53, 54, 54, 57, 57, 59, 59, 61, 61, 63, 63, 67 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

COMMENTS

For a guide to related sequences, see A211266.

LINKS

Table of n, a(n) for n=1..72.

MATHEMATICA

a = 1; b = n; z1 = 120;

t[n_] := t[n] = Flatten[Table[x*y, {x, a, b - 1},

{y, x + 1, b}]]

c[n_, k_] := c[n, k] = Count[t[n], k]

Table[c[n, n], {n, 1, z1}]           (* A056924 *)

Table[c[n, n + 1], {n, 1, z1}]       (* A211159 *)

Table[c[n, 2*n], {n, 1, z1}]         (* A211261 *)

Table[c[n, 3*n], {n, 1, z1}]         (* A211262 *)

Table[c[n, Floor[n/2]], {n, 1, z1}]  (* A211263 *)

Print

c1[n_, m_] := c1[n, m] = Sum[c[n, k], {k, a, m}]

Table[c1[n, n], {n, 1, z1}]          (* A211264 *)

Table[c1[n, n + 1], {n, 1, z1}]      (* A211265 *)

Table[c1[n, 2*n], {n, 1, z1}]        (* A211266 *)

Table[c1[n, 3*n], {n, 1, z1}]        (* A211267 *)

Table[c1[n, Floor[n/2]], {n, 1, z1}] (* A181972 *)

CROSSREFS

Cf. A211266.

Sequence in context: A100881 A053263 A056039 * A058747 A034322 A050365

Adjacent sequences:  A181969 A181970 A181971 * A181973 A181974 A181975

KEYWORD

nonn

AUTHOR

Clark Kimberling, Apr 06 2012

STATUS

approved

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Last modified April 19 17:28 EDT 2014. Contains 240767 sequences.