%I
%S 3,4,10,21,34,46,58,70,85,93,118,129,130,144,178,201,226,237,262,298,
%T 310,322,324,325,333,334,346,382,406,418,430,466,478,502,513,514,517,
%U 549,598,622,633,634,657,658,669,706,730,742,813,826,837,838
%N Numbers n such that the sum of nondivisors of n is prime.
%H Paolo P. Lava, <a href="/A200981/b200981.txt">Table of n, a(n) for n = 1..10000</a>
%e Nondivisors of 10 are 3, 4, 6, 7, 8, 9 and their sum is 37 that is prime.
%p with(numtheory);
%p P:=proc(i)
%p local a,n;
%p for n from 1 to i do
%p a:=n*(n+1)/2sigma(n); if isprime(a) then print(n); fi;
%p od;
%p end:
%p P(1000000);
%t okQ[n_] := (n > 0) && PrimeQ[n]; Select[Range[1000], okQ[# (#+1)/2  DivisorSigma[1, #]] &] (* _T. D. Noe_, Dec 15 2011 *)
%Y Cf. A023194, A024816.
%K nonn,easy
%O 1,1
%A _Paolo P. Lava_, Dec 13 2011
