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%I #23 May 03 2022 08:09:32
%S 0,0,1,0,6,0,1,3,7,0,15,0,8,4,9,0,11,0,14,1,10,0,55,6,15,1,28,0,54,0,
%T 1,9,22,1,17,0,14,1,43,0,66,0,50,15,16,0,64,7,1,11,26,0,78,1,63,1,31,
%U 0,172,0,20,1,41,1,90,0,32,13,40,0,45,0,50,8,63,1,144,0,56,50,40,0,196,1,26,15,76,0,259,11,64,13,43,6,236,0
%N a(n) = s(s(n)), where s(n) = sigma(n)-n = A001065(n).
%H Antti Karttunen, <a href="/A178601/b178601.txt">Table of n, a(n) for n = 2..16384</a>
%H Carl Pomerance, <a href="https://www.semanticscholar.org/paper/THE-FIRST-FUNCTION-AND-ITS-ITERATES-Pomerance/b9ac7d56efb36ca0f44defc231c5b267b4779c97">The first function and its iterates</a>, pp. 125-138 in Connections in Discrete Mathematics, ed. S. Butler et al., Cambridge, 2018.
%H <a href="/index/Su#sums_of_divisors">Index entries for sequences related to sums of divisors</a>
%t Table[Apply[ Plus, Divisors[Apply[ Plus, Divisors[n]] - n]] - (Apply[Plus, Divisors[n]] - n), {n, 0, 100}]
%o (PARI)
%o A001065(n) = (sigma(n) - n);
%o A178601(n) = A001065(A001065(n)); \\ _Antti Karttunen_, Nov 01 2017
%Y Cf. A001065, A000203, A051027, A072869.
%Y Cf. A206708 (fixed points, union of A000396 and A063990). - _Antti Karttunen_, Nov 01 2017
%K nonn
%O 2,5
%A _Roger L. Bagula_, May 30 2010
%E Edited by _N. J. A. Sloane_, May 30 2010
%E Terms a(0) and a(1) removed and more terms added by _Antti Karttunen_, Nov 01 2017
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