A129076 a(n) = sigma(sigma(sigma(sigma(n)))), where sigma(n) = sum of divisors of n.

1, 8, 15, 24, 56, 120, 60, 168, 60, 120, 120, 360, 168, 480, 480, 104, 120, 360, 252, 728, 210, 248, 480, 1512, 104, 728, 546, 1170, 336, 992, 210, 576, 504, 1170, 504, 480, 480, 1512, 1170, 1344, 728, 1680, 504, 1560, 1512, 992, 504, 1560, 384, 432, 992, 588

Offset: 1

Author

Jonathan Vos Post, May 27 2007

Keywords

• easy
• nonn

Comments

a(n) = A000203(A000203(A051027(n))) = A051027(A000203(A000203(n))) = A000203(A051027(A000203(n))) = A000203(A066971(n)) = A066971(A000203(n)) = A051027(A051027(n)). - Jaroslav Krizek, Jul 19 2009

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000203, A051027, A066971.

Cf. A019293.

Programs

Magma

[ SumOfDivisors(SumOfDivisors(SumOfDivisors(SumOfDivisors(n)))) : n in [1..100]];

Mathematica

Nest[DivisorSigma[1,#]&,Range[60],4] (* Harvey P. Dale, Oct 05 2011 *)

PARI

a(n) = sigma(sigma(sigma(sigma(n)))); \\ Michel Marcus, Apr 29 2017

Formula

a(n) = A000203(A000203(A000203(A000203(n)))).