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

Author

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

Keywords

• easy
• nonn
• base

Examples

			a(13)=5 since the 13th prime is 41 and 4+1=5, which is prime.
		

Crossrefs

Cf. A046704.

Programs

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 *)