

A200981


Numbers n such that the sum of nondivisors of n is prime.


2



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
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


LINKS



EXAMPLE

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


MAPLE

with(numtheory);
P:=proc(i)
local a, n;
for n from 1 to i do
a:=n*(n+1)/2sigma(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 *)


CROSSREFS



KEYWORD

nonn,easy


AUTHOR



STATUS

approved



