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%I
%S 22,23,25,27,32,33,35,37,52,53,55,57,72,73,75,77,122,123,125,127,132,
%T 133,135,137,152,153,155,157,172,173,175,177,202,203,205,207,212,213,
%U 215,217,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234
%N Numbers with property that number of prime digits is prime.
%C A subset of A085557 from the 4th term.
%C Upper relative density in the primes is 1; lower relative density in the primes is 0. [From _Charles R Greathouse IV_, Nov 14 2010]
%e 22 has two prime digits and their number 2 is prime,
%e 222 has three prime digits and their number 3 is prime.
%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:=proc(n) local i, stpf, ans, ans1; ans:=[ ]: stpf:=0: for i from 1 to n do if (isprime( ts_stpf(i) )='true') then ans:=[ op(ans), i ]: fi od; RETURN(ans) end: ts_pr(300);
%t Select[Range[250],PrimeQ[Count[IntegerDigits[#],_?PrimeQ]]&] (* From Harvey P. Dale, Nov 29 2011 *)
%K nonn,base,changed
%O 1,1
%A _Jani Melik_, Apr 11 2004
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