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%I #11 May 07 2019 23:39:45
%S 13,17,29,31,59,71,79,97,103,107,163,167,241,269,281,349,389,421,431,
%T 439,479,509,541,569,613,617,631,659,701,709,761,769,821,829,839,859,
%U 907,947,967,983,1063,1087,1123,1153,1213,1217,1229,1231,1259,1279,1297
%N Primes with the same number of decimal digits that are {1, 9} as {2, 3, 5, 7}.
%C Primes with the same number of prime decimal digits as odd nonprime digits.
%p digs1or9 := proc(n) local a,c; a := 0 ; for c in convert(n,base,10) do if c in {1,9} then a := a+1 ; end if; end do; a; end proc: A109066 := proc(n) local a,d; p := ithprime(n) ; a := 0 ; for d in convert(p,base,10) do if isprime(d) then a := a+1 ; end if; end do; a; end proc: for n from 1 to 400 do p := ithprime(n) ; if digs1or9(p) = A109066(n) then printf("%d,",p) ; fi; od: # _R. J. Mathar_, Oct 22 2009
%t ddQ[n_]:=Module[{idn=IntegerDigits[n]},Count[idn,1|9]==Count[idn, 2|3|5|7]]; Select[Prime[Range[250]],ddQ] (* _Harvey P. Dale_, Nov 29 2011 *)
%K nonn,base
%O 1,1
%A _Juri-Stepan Gerasimov_, Jan 15 2009
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