A067134 Numbers n such that sigma(n+1) = 2*sigma(n-1).

119, 1559, 2939, 17759, 19919, 32219, 33839, 55964, 71039, 186779, 308039, 511499, 523775, 553499, 699359, 838214, 1048904, 1159379, 1328939, 1333247, 1700039, 2462687, 2703887, 2956079, 3115319, 3561095, 3764207, 3972695, 7625879, 7852919, 8048963

Offset: 1

Author

Benoit Cloitre, Feb 18 2002

Keywords

• nonn

Comments

For each term given here, n+1 is divisible by 3, but that's not always true; n=12396999 is a counterexample.

Links

• Donovan Johnson, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A055574, A067135.

Programs

Mathematica

Flatten[Position[Partition[DivisorSigma[1,Range[8100000]],3,1],?(Last[#] == 2*First[#]&),{1},Heads->False]]+1 (* _Harvey P. Dale, Aug 19 2013 *)

PARI

s1=1; s2=3; for(n=2, 10^8, s3=sigma(n+1); if(s3==2*s1, print1(n ", ")); s1=s2; s2=s3) /* Donovan Johnson, Apr 06 2013 */

Extensions

Edited by Dean Hickerson, Feb 20 2002