OFFSET
1,1
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
The divisors of 28 are {1, 2, 4, 7, 14, 28} and the sum of its nonprime divisors is 1 + 4 + 14 + 28 = 47 is prime, hence 28 is in the sequence.
MAPLE
with(numtheory): for n from 1 to 435 do x:=divisors(n): n1:=nops(x): s:=0: for k from 1 to n1 do if not isprime(x[k]) then s:=s+x[k] fi od: if isprime(s) then printf(`%d, `, n) fi od:
MATHEMATICA
f[n_] := Plus @@ Select[Divisors[n], ! PrimeQ[#] &]; Select[Range[435], PrimeQ[f[#]] &] (* T. D. Noe, Aug 29 2011 *)
PROG
(PARI) isok(n) = isprime(sumdiv(n, d, if (!isprime(d), d))); \\ Michel Marcus, Jan 07 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Lagneau, Aug 29 2011
STATUS
approved