cp's OEIS Frontend

A376156 a(n) is the least number that is the sum of the nonprime divisors of k for exactly n different k.

%I A376156 #4 Sep 13 2024 08:07:25
%S A376156 2,5,23,83,536,2519,45359,16736,743398,1908958,3386606,9295535
%N A376156 a(n) is the least number that is the sum of the nonprime divisors of k for exactly n different k.
%e A376156 2 is not the sum of the nonprime divisors of any k.
%e A376156 5 is the sum of the nonprime divisors of 4 (1 + 4 = 5).
%e A376156 23 is the sum of the nonprime divisors of 12 (1 + 4 + 6 + 12) and of 22 (1 + 22).
%e A376156 83 is the sum of the nonprime divisors of 40 (1 + 4 + 8 + 10 + 20 + 40) and 52 (1 + 4 + 26 + 52) and 82 (1 + 82).
%p A376156 N:= 10^6: # for terms < 10^6
%p A376156 f:= proc(n) convert(remove(isprime, numtheory:-divisors(n)),`+`) end proc:
%p A376156 R:= Vector(N):
%p A376156 for i from 1 to N do
%p A376156   v:= f(i);
%p A376156   if v <= N then R[v]:= R[v]+1 fi
%p A376156 od:
%p A376156 m:= convert(R,set)[-2]:
%p A376156 V:= Array(0..m): count:= 0:
%p A376156 for i from 2 while count < m+1 do
%p A376156 if V[R[i]] = 0 then V[R[i]]:= i; count:= count+1 fi
%p A376156 od:
%p A376156 convert(V,list);
%Y A376156 Cf. A023890.
%K A376156 nonn,more
%O A376156 0,1
%A A376156 _Robert Israel_, Sep 12 2024