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Semiprimes with odd digits.
4

%I #17 Mar 20 2015 03:16:03

%S 9,15,33,35,39,51,55,57,77,91,93,95,111,115,119,133,155,159,177,319,

%T 335,339,355,371,377,391,393,395,511,515,517,519,533,535,537,551,553,

%U 559,573,579,591,597,713,717,731,737,753,755,771,779,791,793,799,913,917

%N Semiprimes with odd digits.

%C Semiprimes with odd digits are more numerous than those with even digits, cf. A108636.

%t Select[Range[1000], Plus@@Last/@FactorInteger[ # ]==2&&Union[OddQ/@IntegerDigits[ # ]]=={True}&]

%t PrimeFactorExponentsAdded[n_] := Plus @@ Flatten[ Table[ #[[2]], {1}] & /@ FactorInteger[n]]; Select[ Range[ 938], PrimeFactorExponentsAdded[ # ] == 2 && Union[ OddQ /@ IntegerDigits[ # ]] == {True} &] (* _Robert G. Wilson v_ *)

%t Select[Range[1000], PrimeOmega[#]==2 && And@@OddQ[IntegerDigits[#]]&] (* _Harvey P. Dale_, Jul 12 2011 *)

%Y Cf. A001358 (semiprimes), A108636.

%K easy,nonn,base

%O 1,1

%A _Zak Seidov_, Feb 22 2004

%E Corrected and extended by _Ray Chandler_ and _Robert G. Wilson v_, Feb 25 2004

%E Edited by _N. J. A. Sloane_, Apr 20 2007