%I #4 Mar 31 2012 14:40:00

%S 23,37,53,73,127,137,157,173,229,239,251,263,271,283,293,307,313,317,

%T 331,347,359,367,379,383,397,433,457,503,521,547,563,571,587,593,653,

%U 673,677,739,743,751,787,797,823,827,853,857,877,937,953,977,1033,1123

%N Primes with exactly two prime digits.

%F a(n) >> n^1.285

%e 23 is prime and it has two prime digits, 2 and 3;

%e 127 is prime and it has two prime digits 2 and 7.

%p stev_sez:=proc(n) local i, tren, st, ans, anstren; ans:=[ ]: anstren:=[ ]: tren:=n: for i while (tren>0) do st:=round( 10*frac(tren/10) ): ans:=[ op(ans), st ]: tren:=trunc(tren/10): end do; for i from nops(ans) to 1 by -1 do anstren:=[ op(anstren), op(i,ans) ]; od; RETURN(anstren); end: ts_stpf:=proc(n) local i, stpf, ans; ans:=stev_sez(n): stpf:=0: for i from 1 to nops(ans) do if (isprime(op(i,ans))='true') then stpf:=stpf+1; # number of prime digits fi od; RETURN(stpf) end: ts_pr_prnd:=proc(n) local i, stpf, ans, ans1, tren; ans:=[ ]: stpf:=0: tren:=1: for i from 1 to n do if ( isprime(i)='true' and ts_stpf(i) = 2) then ans:=[ op(ans), i ]: tren:=tren+1; fi od; RETURN(ans) end: ts_pr_prnd(2500);

%Y Cf. A034844.

%K nonn,base

%O 1,1

%A _Jani Melik_, Apr 11 2004