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

14, 118, 3, 2

Offset: 1

Author

Zak Seidov, Oct 06 2010

Keywords

• more
• nonn

Comments

a(1)= A002961(1).

a(2)= A175876(1), a(3)= A175875(1). - Zak Seidov, Jul 07 2013

Is n = 2 the only solution for sigma(n+4)=4*sigma(n)? - Zak Seidov, Jul 07 2013

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

Examples

			sigma(14+1)/sigma(14)=24/24=1, sigma(118+2)/sigma(118)=360/180=2,
sigma(3+3)/sigma(3)=12/4=3, sigma(4+4)/sigma(2)=12/3=4.
		

Crossrefs

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

Cf. A175875, A175876. - Zak Seidov, Jul 07 2013