Search: id:A123930
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%I A123930
%S A123930 2,3,6,21,31,31,49,73,73,91,115,121,121,121,169,169,211,211,211,211,211,
%T A123930 301,331,331,331,361,391,391,421,421,421,421,421,511,511,631,631,631,
%U A123930 631,631,631,631,721,721,721,781,781,841,841,841,841,841,841,841,841
%N A123930 a(n) = smallest k > 1 that is the sum of the proper divisors (cf. A001065) 
               of at least n different numbers.
%H A123930 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               RestrictedDivisorFunction.html">Sum of Proper Divisors Function</
               a>.
%e A123930 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 A123930 (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 A123930 Cf. A001065, A070015, A048138, A125601.
%Y A123930 Sequence in context: A093447 A002078 A000372 this_sequence A125601 A025239 
               A127294
%Y A123930 Adjacent sequences: A123927 A123928 A123929 this_sequence A123931 A123932 
               A123933
%K A123930 nonn
%O A123930 0,1
%A A123930 Sergio Pimentel (ferdiego(AT)cox.net), Nov 22 2006
%E A123930 Edited and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), 
               Nov 27 2006

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