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%I #8 Jan 04 2014 19:48:26
%S 2,3,6,21,31,31,49,73,73,91,115,121,121,121,169,169,211,211,211,211,
%T 211,301,331,331,331,361,391,391,421,421,421,421,421,511,511,631,631,
%U 631,631,631,631,631,721,721,721,781,781,841,841,841,841,841,841,841,841
%N a(n) = smallest k > 1 that is the sum of the proper divisors (cf. A001065) of at least n different numbers.
%H Donovan Johnson, <a href="/A123930/b123930.txt">Table of n, a(n) for n = 0..1000</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/RestrictedDivisorFunction.html">Sum of Proper Divisors Function</a>.
%e a(0)=2 because 2 is the smallest number that is not the sum of proper divisors of any number (untouchable). a(6)=49 since 49 is the smallest number that is the sum of proper divisors of 6 different numbers (75, 215, 287, 407, 527, 551).
%o (PARI) {z=850;m=200000;v=vector(z);for(n=2,m,s=sigma(n)-n;if(s<z,v[s]++));r=0;for(j=2,z, while(r<=v[j],r=r+1;print1(j,",")))} \\ _Klaus Brockhaus_, Nov 27 2006
%Y Cf. A001065, A070015, A048138, A125601.
%K nonn
%O 0,1
%A _Sergio Pimentel_, Nov 22 2006
%E Edited and extended by _Klaus Brockhaus_, Nov 27 2006
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