A175875 -id:A175875 - cp's OEIS frontend

A175876 Numbers k such that sigma(k+2) = 2*sigma(k).

118, 1558, 2938, 17758, 19918, 32218, 33838, 55963, 71038, 186778, 308038, 511498, 523774, 553498, 699358, 838213, 1048903, 1159378, 1328938, 1333246, 1700038, 2462686, 2703886, 2956078, 3115318, 3561094, 3764206, 3972694, 7625878, 7852918, 8048962

Offset: 1

Zak Seidov, Oct 06 2010

nonn

a(1) = A175874(2).

Vincenzo Librandi and Donovan Johnson, Table of n, a(n) for n = 1..1000 (first 171 terms from Vincenzo Librandi)

Cf. A000203, A002961, A175874, A175875.

Do[If[DivisorSigma[1, n+2]==2 DivisorSigma[1, n], Print[n]], {n, 2, 10^7}] (* or *) Select[Range[8000000], DivisorSigma[1, # + 2] == 2 DivisorSigma[1, #]&](* Vincenzo Librandi, Apr 04 2013 *)

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

Original entry on oeis.org

14, 118, 3, 2

Offset: 1

Zak Seidov, Oct 06 2010

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

			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.

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

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

cp's OEIS Frontend

A175876 Numbers k such that sigma(k+2) = 2*sigma(k).

Views

Author

Keywords

Comments

Links

Crossrefs

Programs

Mathematica