

A123930


a(n) = smallest k > 1 that is the sum of the proper divisors (cf. A001065) of at least n different numbers.


2



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
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OFFSET

0,1


LINKS



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).


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


CROSSREFS



KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



