A123930 a(n) = smallest k > 1 that is the sum of the proper divisors (cf. A001065) of at least n different numbers.

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

Offset: 0

Author

Sergio Pimentel, Nov 22 2006

Keywords

• nonn

Examples

			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).
		

Links

• Donovan Johnson, Table of n, a(n) for n = 0..1000
• Eric Weisstein's World of Mathematics, Sum of Proper Divisors Function.

Crossrefs

Cf. A001065, A070015, A048138, A125601.

Programs

PARI

{z=850;m=200000;v=vector(z);for(n=2,m,s=sigma(n)-n;if(sKlaus Brockhaus, Nov 27 2006

Extensions

Edited and extended by Klaus Brockhaus, Nov 27 2006