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A068951
Scan the primes, record digit-sum if it is itself prime.
1
2, 3, 5, 7, 2, 5, 11, 5, 7, 11, 7, 13, 11, 17, 2, 5, 5, 11, 13, 7, 13, 11, 17, 11, 13, 17, 19, 7, 11, 13, 7, 11, 17, 11, 13, 5, 7, 11, 7, 13, 11, 17, 13, 19, 19, 5, 13, 7, 11, 17, 11, 13, 17, 19, 17, 13, 19, 17, 23, 7, 13, 11, 13, 17, 13, 17, 17, 13, 19, 13, 19, 17, 23, 17, 11, 13
OFFSET
1,1
EXAMPLE
a(13)=5 since the 13th prime is 41 and 4+1=5, which is prime.
MAPLE
dig := X->convert((convert(X, base, 10)), `+`); a := n->`if`(isprime(dig(ithprime(n)))=true, dig(ithprime(n)), printf(""));
MATHEMATICA
Select[Total[IntegerDigits[#]]&/@Prime[Range[200]], PrimeQ] (* Harvey P. Dale, Oct 17 2020 *)
CROSSREFS
Cf. A046704.
Sequence in context: A007605 A077765 A078400 * A139752 A238191 A004088
KEYWORD
easy,nonn,base
AUTHOR
Francois Jooste (phukraut(AT)hotmail.com), Mar 10 2002
STATUS
approved