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%I #7 Dec 27 2013 15:21:04
%S 4,6,9,14,22,25,33,35,55,57,77,91,119,122,123,133,141,155,161,177,213,
%T 215,217,221,321,371,411,515,517,551,611,713,717,721,731,771,1114,
%U 1119,1133,1135,1137,1141,1157,1177,1191,1271,1313,1315,1317,1351,1371,1411
%N Semiprimes for which the product of the digits is also a semiprime.
%H Harvey P. Dale, <a href="/A118689/b118689.txt">Table of n, a(n) for n = 1..300</a>
%e 77 is in the sequence because (1 )it is a semiprime and (2) the product of its digits 7*7=49 is also a semiprime.
%t Select[Range[2000],PrimeOmega[#]==PrimeOmega[Times@@IntegerDigits[#]] == 2&] (* _Harvey P. Dale_, Dec 27 2013 *)
%o (PARI) A007954(n)= { local(resul) ; if(n==0, return(0) ; ) ; resul= 1 ; while(n>0, resul *= n%10 ; n = (n-n%10)/10 ; ) ; return(resul) ; } { for(n=4,2000, if( bigomega(n)==2, if(A007954(n) != 0 && bigomega(A007954(n)) == 2, print1(n,","); ) ; ) ; ) ; } - _R. J. Mathar_, Aug 21 2006
%Y Cf. A001358.
%K base,nonn
%O 1,1
%A Luc Stevens (lms022(AT)yahoo.com), May 20 2006
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