cp's OEIS Frontend

A249447 Least n-digit prime whose digit sum is also prime.

%I A249447 #18 Oct 30 2014 11:51:53
%S A249447 2,11,101,1013,10037,100019,1000033,10000019,100000037,1000000033,
%T A249447 10000000019,100000000019,1000000000039,10000000000037,
%U A249447 100000000000031,1000000000000037,10000000000000079,100000000000000013,1000000000000000031,10000000000000000051,100000000000000000039
%N A249447 Least n-digit prime whose digit sum is also prime.
%C A249447 Subsequence of A046704 (primes with digits sum being prime).
%C A249447 Some terms of this sequence are also in A003617, the least n-digit primes. - _Michel Marcus_, Oct 30 2014
%H A249447 Paolo P. Lava, <a href="/A249447/b249447.txt">Table of n, a(n) for n = 1..100</a>
%e A249447 a(1) = 2 because it is the least prime with just one digit.
%e A249447 a(2) = 11 because it is the least prime with 2 digits whose sum, 1 + 1 = 2, is a prime.
%e A249447 Again, a(7) = 1000033 because it is the least prime with 7 digits whose sum is a prime: 1 + 0 + 0 + 0 + 0 + 3 + 3 = 7.
%p A249447 P:=proc(q) local a,b,k,n; for k from 0 to q do
%p A249447 for n from 10^k to 10^(k+1)-1 do if isprime(n) then a:=n; b:=0;
%p A249447 while a>0 do b:=b+(a mod 10); a:=trunc(a/10); od;
%p A249447 if isprime(b) then print(n); break; fi; fi;
%p A249447 od; od; end: P(10^3);
%o A249447 (PARI) a(n) = {p = nextprime(10^(n-1)); while (!isprime(sumdigits(p)), p = nextprime(p+1)); p;} \\ _Michel Marcus_, Oct 29 2014
%Y A249447 Cf. A003617, A046704, A068166, A249448.
%K A249447 nonn,base
%O A249447 1,1
%A A249447 _Paolo P. Lava_, Oct 29 2014