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a(n) = sigma(sigma(sigma(sigma(n)))), where sigma(n) = sum of divisors of n.
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%I #20 Sep 08 2022 08:45:30

%S 1,8,15,24,56,120,60,168,60,120,120,360,168,480,480,104,120,360,252,

%T 728,210,248,480,1512,104,728,546,1170,336,992,210,576,504,1170,504,

%U 480,480,1512,1170,1344,728,1680,504,1560,1512,992,504,1560,384,432,992,588

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

%C 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

%H Harvey P. Dale, <a href="/A129076/b129076.txt">Table of n, a(n) for n = 1..1000</a>

%F a(n) = A000203(A000203(A000203(A000203(n)))).

%t Nest[DivisorSigma[1,#]&,Range[60],4] (* _Harvey P. Dale_, Oct 05 2011 *)

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

%o (PARI) a(n) = sigma(sigma(sigma(sigma(n)))); \\ _Michel Marcus_, Apr 29 2017

%Y Cf. A000203, A051027, A066971.

%Y Cf. A019293.

%K easy,nonn

%O 1,2

%A _Jonathan Vos Post_, May 27 2007