A067065 Numbers k such that sigma(sigma(sigma(k))) == 6*sigma(k).

20, 26, 41, 44, 65, 83, 132, 133, 140, 182, 188, 195, 249, 287, 299, 420, 546, 564, 620, 644, 764, 806, 861, 897, 1001, 1115, 1169, 1271, 28644, 32172, 35052, 39116, 40796, 41478, 42315, 47492, 50162, 51513, 52143, 53745, 54033, 54483, 56427, 56642

Offset

1,1

Links

Harry J. Smith, Table of n, a(n) for n = 1..146

Mathematica

Select[Range[60000], Nest[DivisorSigma[1, #]&, #, 3]==6*DivisorSigma[1, #]&] (* Harvey P. Dale, Oct 04 2016 *)

Prog

(PARI) isok(k) = { sigma(sigma(sigma(k))) == 6*sigma(k) } \\ Harry J. Smith, May 03 2010

Crossrefs

Sequence in context: A252660 A265401 A276503 * A280307 A101070 A219805

Adjacent sequences: A067062 A067063 A067064 * A067066 A067067 A067068

Keyword

nonn

Author

Benoit Cloitre, Feb 17 2002

Extensions

Definition corrected by Harry J. Smith, May 03 2010

Terms added by Harry J. Smith, May 03 2010

Status

approved