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a(n) = sigma(sigma(sigma(sigma(sigma(n))))).
1

%I #19 Nov 20 2017 05:36:02

%S 1,15,24,60,120,360,168,480,168,360,360,1170,480,1512,1512,210,360,

%T 1170,728,1680,576,480,1512,4800,210,1680,1344,3276,992,2016,576,1651,

%U 1560,3276,1560,1512,1512,4800,3276,4064,1680,5952,1560,5040,4800,2016,1560,5040

%N a(n) = sigma(sigma(sigma(sigma(sigma(n))))).

%H Antti Karttunen, <a href="/A162964/b162964.txt">Table of n, a(n) for n = 1..16384</a>

%H <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>

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

%p with(numtheory); f:=n->sigma(sigma(sigma(sigma(sigma(n))))); [seq(f(n),n=1..100)];

%t Table[Nest[DivisorSigma[1,#]&,n,5],{n,50}] (* _Harvey P. Dale_, Apr 19 2013 *)

%o (PARI) A162964(n) = sigma(sigma(sigma(sigma(sigma(n))))); \\ _Antti Karttunen_, Nov 18 2017

%Y Cf. A000203, A129076, A066971, A051027.

%Y Cf. also A049107.

%K nonn

%O 1,2

%A _Jaroslav Krizek_, Jul 19 2009

%E More terms from _N. J. A. Sloane_, Mar 20 2010