A154762 Primes with the same number of decimal digits that are {1, 9} as {2, 3, 5, 7}.

13, 17, 29, 31, 59, 71, 79, 97, 103, 107, 163, 167, 241, 269, 281, 349, 389, 421, 431, 439, 479, 509, 541, 569, 613, 617, 631, 659, 701, 709, 761, 769, 821, 829, 839, 859, 907, 947, 967, 983, 1063, 1087, 1123, 1153, 1213, 1217, 1229, 1231, 1259, 1279, 1297

Offset: 1

Author

Juri-Stepan Gerasimov, Jan 15 2009

Keywords

• nonn
• base

Comments

Primes with the same number of prime decimal digits as odd nonprime digits.

Programs

Maple

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

Mathematica

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 *)