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

3, 4, 10, 21, 34, 46, 58, 70, 85, 93, 118, 129, 130, 144, 178, 201, 226, 237, 262, 298, 310, 322, 324, 325, 333, 334, 346, 382, 406, 418, 430, 466, 478, 502, 513, 514, 517, 549, 598, 622, 633, 634, 657, 658, 669, 706, 730, 742, 813, 826, 837, 838

Offset: 1

Author

Paolo P. Lava, Dec 13 2011

Keywords

• nonn
• easy

Examples

			Non-divisors of 10 are 3, 4, 6, 7, 8, 9 and their sum is 37 that is prime.
		

Links

• Paolo P. Lava, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A023194, A024816.

Programs

Maple

with(numtheory);
P:=proc(i)
local a,n;
for n from 1 to i do
  a:=n*(n+1)/2-sigma(n); if isprime(a) then print(n); fi;
od;
end:
P(1000000);

Mathematica

okQ[n_] := (n > 0) && PrimeQ[n]; Select[Range[1000], okQ[# (#+1)/2 - DivisorSigma[1, #]] &] (* T. D. Noe, Dec 15 2011 *)