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A070015 Least m such that the sum of the aliquot parts of m (A001065) equals n, or 0 if no such number exists. 9

%I

%S 2,0,4,9,0,6,8,10,15,14,21,121,27,22,16,12,39,289,65,34,18,20,57,529,

%T 95,46,69,28,115,841,32,58,45,62,93,24,155,1369,217,44,63,30,50,82,

%U 123,52,129,2209,75,40,141,0,235,42,36,106,99,68,265,3481,371,118,64,56

%N Least m such that the sum of the aliquot parts of m (A001065) equals n, or 0 if no such number exists.

%H Robert G. Wilson v, <a href="/A070015/b070015.txt">Table of n, a(n) for n = 1..10000</a> (first 9884 terms from Richard J. Mathar)

%H Mersenne Forum, <a href="http://www.mersenneforum.org/showthread.php?t=18379">Given sigma(n)-n, find the smallest possible n</a>

%F a(n) = min(x, A001065(x)=n) or a(n)=0 if n is an untouchable number (i.e., if from A005114).

%e For n=128: a(128)=16129, divisors={1,127,16129}, 1+127=sigma(n)-n=128 and 16129 is the smallest.

%t f[x_] := DivisorSigma[1, x]-x; t=Table[0, {128}]; Do[c=f[n]; If[c<129&&t[[c]]==0, t[[c]]=n], {n, 1000000}]; t

%Y Cf. A000203, A001065, A048050, A051444, A007369, A070016, A005114, A048995.

%K nonn,changed

%O 1,1

%A _Labos Elemer_, Apr 12 2002

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Last modified April 5 20:24 EDT 2020. Contains 333260 sequences. (Running on oeis4.)