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A139799 Integers k with at least one divisor d > 1 that divides (n/d)+1. 1
2, 6, 10, 12, 14, 15, 18, 20, 22, 24, 26, 28, 30, 33, 34, 38, 42, 44, 45, 46, 50, 51, 54, 56, 58, 60, 62, 66, 69, 70, 72, 74, 76, 78, 82, 86, 87, 90, 91, 92, 94, 95, 96, 98, 102, 105, 106, 108, 110, 114, 118, 120, 122, 123, 124, 126, 130, 132, 134, 138, 140 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Previous name: Sequence of integers n>=2 such that there is an integer k>1 with k divides n and k divides (n/k)+1.

The first square in the sequence is 1225.

First squares are 1225, 8100, 25600, 46225. - Zak Seidov, Nov 14 2012

LINKS

Zak Seidov, Table of n, a(n) for n = 1..10000

J. Malenfant, On the Matrix-Element Expansion of a Circulant Determinant, arXiv preprint arXiv:1502.06012 [math.NT], 2015.

EXAMPLE

2 is a term since 2 divides 2 and 2/2 + 1.

6 is a term since 3 divides 6 and 6/3 + 1.

MATHEMATICA

okQ[n_] := Sum[Divisible[n/d+1, d] // Boole, {d, Divisors[n] // Rest}] > 0;

Select[Range[140], okQ] (* Jean-Fran├žois Alcover, Aug 10 2018 *)

PROG

(PARI) isok(n) = sumdiv(n, d, (d>1) && !(((n/d)+1) % d)) >= 1; \\ Michel Marcus, May 08 2018

CROSSREFS

Sequence in context: A133520 A099017 A298748 * A214586 A305634 A139710

Adjacent sequences:  A139796 A139797 A139798 * A139800 A139801 A139802

KEYWORD

nonn

AUTHOR

Juan Lopez Gonzalez (e44625(AT)estudiante.uam.es), Jun 14 2008

EXTENSIONS

Number 37 corrected to 38 by Zak Seidov, Nov 14 2012

New name from Michel Marcus, May 08 2018

STATUS

approved

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Last modified July 12 18:03 EDT 2020. Contains 335666 sequences. (Running on oeis4.)