OFFSET
1,1
LINKS
Paolo P. Lava, Table of n, a(n) for n = 1..10000
EXAMPLE
Non-divisors 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)/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 *)
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paolo P. Lava, Dec 13 2011
STATUS
approved