OFFSET
1,1
FORMULA
(a(n) mod 9) mod 2 = 0. - Altug Alkan, Sep 28 2015
EXAMPLE
11 (prime) + 2 (its digital root) = 13 (prime);
89 (prime) + 8 (its digital root) = 97 (prime).
MATHEMATICA
Select[Prime[Range[300]], PrimeQ[# + Mod[#, 9]] &] (* Vincenzo Librandi, Sep 29 2015 *)
PROG
(PARI) lista(nn) = forprime(p=2, nn, if (isprime(p + p%9), print1(p, ", "))); \\ Michel Marcus, Sep 12 2015
(Magma) [p: p in PrimesUpTo(2000) | IsPrime(p+(p mod 9))]; // Vincenzo Librandi, Sep 29 2015
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Gary Croft, Sep 11 2015
STATUS
approved