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A200981 Numbers n such that the sum of non-divisors of n is prime. 2

%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 non-divisors of n is prime.

%H Paolo P. Lava, <a href="/A200981/b200981.txt">Table of n, a(n) for n = 1..10000</a>

%e Non-divisors 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)/2-sigma(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

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Last modified March 19 17:19 EDT 2019. Contains 321330 sequences. (Running on oeis4.)