A068951 Scan the primes, record digit-sum if it is itself prime.

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

Links

Table of n, a(n) for n=1..76.

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

Adjacent sequences: A068948 A068949 A068950 * A068952 A068953 A068954

Keyword

easy,nonn,base

Author

Francois Jooste (phukraut(AT)hotmail.com), Mar 10 2002

Status

approved