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 A139799 Integers k with at least one divisor d > 1 that divides (n/d)+1. 1

%I

%S 2,6,10,12,14,15,18,20,22,24,26,28,30,33,34,38,42,44,45,46,50,51,54,

%T 56,58,60,62,66,69,70,72,74,76,78,82,86,87,90,91,92,94,95,96,98,102,

%U 105,106,108,110,114,118,120,122,123,124,126,130,132,134,138,140

%N Integers k with at least one divisor d > 1 that divides (n/d)+1.

%C 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.

%C The first square in the sequence is 1225.

%C First squares are 1225, 8100, 25600, 46225. - _Zak Seidov_, Nov 14 2012

%H Zak Seidov, <a href="/A139799/b139799.txt">Table of n, a(n) for n = 1..10000</a>

%H J. Malenfant, <a href="http://arxiv.org/abs/1502.06012">On the Matrix-Element Expansion of a Circulant Determinant</a>, arXiv preprint arXiv:1502.06012 [math.NT], 2015.

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

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

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

%t Select[Range[140], okQ] (* _Jean-François Alcover_, Aug 10 2018 *)

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

%K nonn

%O 1,1

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

%E Number 37 corrected to 38 by _Zak Seidov_, Nov 14 2012

%E New name from _Michel Marcus_, May 08 2018

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Last modified August 4 13:24 EDT 2020. Contains 336201 sequences. (Running on oeis4.)