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A211159 Number of integer pairs (x,y) such that 0<x<y<=n and x*y=n+1. 9
0, 0, 0, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 1, 1, 0, 2, 0, 2, 1, 1, 0, 3, 0, 1, 1, 2, 0, 3, 0, 2, 1, 1, 1, 3, 0, 1, 1, 3, 0, 3, 0, 2, 2, 1, 0, 4, 0, 2, 1, 2, 0, 3, 1, 3, 1, 1, 0, 5, 0, 1, 2, 2, 1, 3, 0, 2, 1, 3, 0, 5, 0, 1, 2, 2, 1, 3, 0, 4, 1, 1, 0, 5, 1, 1, 1, 3, 0, 5, 1, 2, 1, 1, 1, 5, 0, 2, 2, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,11

COMMENTS

For a guide to related sequences, see A211266.

LINKS

Table of n, a(n) for n=1..99.

EXAMPLE

a(11) counts these pairs:  (2,6), (3,4).

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 *)

Cf. A211266.

CROSSREFS

Sequence in context: A084114 A110475 A086971 * A088434 A205745 A243223

Adjacent sequences:  A211156 A211157 A211158 * A211160 A211161 A211162

KEYWORD

nonn

AUTHOR

Clark Kimberling, Apr 06 2012

STATUS

approved

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Last modified November 25 18:10 EST 2014. Contains 250000 sequences.