|
%I #5 Oct 17 2020 18:15:52
%S 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,
%T 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,
%U 17,19,17,13,19,17,23,7,13,11,13,17,13,17,17,13,19,13,19,17,23,17,11,13
%N Scan the primes, record digit-sum if it is itself prime.
%e a(13)=5 since the 13th prime is 41 and 4+1=5, which is prime.
%p dig := X->convert((convert(X,base,10)),`+`); a := n->`if`(isprime(dig(ithprime(n)))=true,dig(ithprime(n)),printf(""));
%t Select[Total[IntegerDigits[#]]&/@Prime[Range[200]],PrimeQ] (* _Harvey P. Dale_, Oct 17 2020 *)
%Y Cf. A046704.
%K easy,nonn,base
%O 1,1
%A Francois Jooste (phukraut(AT)hotmail.com), Mar 10 2002
|
