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A175874 a(n) = least number such that sigma(a(n)+n)=n*sigma(a(n)). 2

%I

%S 14,118,3,2

%N a(n) = least number such that sigma(a(n)+n)=n*sigma(a(n)).

%C a(1)= A002961(1).

%C a(2)= A175876(1), a(3)= A175875(1). - _Zak Seidov_, Jul 07 2013

%C Is n = 2 the only solution for sigma(n+4)=4*sigma(n)? - _Zak Seidov_, Jul 07 2013

%C A further solution to sigma(n+4)=4*sigma(n), and the terms a(5) and a(6), if they exist, they are all larger than 3*10^12. - _Giovanni Resta_, Jun 06 2016

%e sigma(14+1)/sigma(14)=24/24=1, sigma(118+2)/sigma(118)=360/180=2,

%e sigma(3+3)/sigma(3)=12/4=3, sigma(4+4)/sigma(2)=12/3=4.

%Y Cf. A000203 sigma(n), A002961 sigma(n) = sigma(n+1).

%Y Cf. A175875, A175876. - _Zak Seidov_, Jul 07 2013

%K more,nonn

%O 1,1

%A _Zak Seidov_, Oct 06 2010

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Last modified January 24 01:20 EST 2021. Contains 340398 sequences. (Running on oeis4.)