A231170 - OEIS

%I #16 May 05 2014 16:18:45

%S 10,14,21,25,34,38,49,58,65,69,74,85,87,94,1003,1007,1018,1027,1041,

%T 1043,1047,1067,1081,1094,1126,1142,1186,1203,1205,1207,1214,1227,

%U 1234,1238,1241,1243,1247,1261,1263,1267,1285,1294,1306,1322,1346,1366,1382,1401

%N Semiprimes with equal number of even and odd digits.

%C This is to A144226 as semiprimes A001358 are to primes A000040.

%H T. D. Noe, <a href="/A231170/b231170.txt">Table of n, a(n) for n = 1..10000</a>

%F A001358 INTERSECTION A227870.

%t semiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; fQ[n_] := Module[{d = IntegerDigits[n], len}, len = Length[d]; EvenQ[len] && len == 2*Count[d, _?(EvenQ[#] &)]]; Select[Range[2500], semiPrimeQ[#] && fQ[#] &] (* _T. D. Noe_, Nov 07 2013 *)

%t Select[Range[2500],PrimeOmega[#]==2&&Count[IntegerDigits[#],_?OddQ] == IntegerLength[#]/2&] (* _Harvey P. Dale_, May 05 2014 *)

%Y Cf. A001358, A030141, A031443, A144226, A227870.

%K nonn,base,easy

%O 1,1

%A _Jonathan Vos Post_, Nov 04 2013

%E More terms from _Alois P. Heinz_, Nov 07 2013