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A123930
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a(n) = smallest k > 1 that is the sum of the proper divisors (cf. A001065) of at least n different numbers.
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1
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2, 3, 6, 21, 31, 31, 49, 73, 73, 91, 115, 121, 121, 121, 169, 169, 211, 211, 211, 211, 211, 301, 331, 331, 331, 361, 391, 391, 421, 421, 421, 421, 421, 511, 511, 631, 631, 631, 631, 631, 631, 631, 721, 721, 721, 781, 781, 841, 841, 841, 841, 841, 841, 841, 841
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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LINKS
| Eric Weisstein's World of Mathematics, Sum of Proper Divisors Function.
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EXAMPLE
| 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).
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PROG
| (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
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CROSSREFS
| Cf. A001065, A070015, A048138, A125601.
Sequence in context: A168268 A002078 A000372 * A125601 A025239 A127294
Adjacent sequences: A123927 A123928 A123929 * A123931 A123932 A123933
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KEYWORD
| nonn
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AUTHOR
| Sergio Pimentel (ferdiego(AT)cox.net), Nov 22 2006
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EXTENSIONS
| Edited and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), Nov 27 2006
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