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%I #22 Jul 09 2015 06:02:24
%S 4,6,9,15,22,33,46,51,55,69,77,82,86,87,91,95,118,121,123,141,145,158,
%T 159,177,185,194,202,213,217,226,235,249,253,262,267,301,303,321,329,
%U 334,339,361,365,393,411,415,437,446,447,451,473,482,489,501,505,514
%N Semiprimes for which the sum of the digits is also a semiprime.
%C The first term congruent to 2 mod 9 is a(2729) = 29999. - _Robert Israel_, Jul 07 2015
%C Among first 10000 terms, numbers of terms congruent to {0..8} mod 9 are: {1,425,139,1453,2773,1233,1252,3087,2739}. Terms with minimal digitsum = 4 are: {4,22,121,202,301,1003,1111,2101,10003, 10021,10102,10201,11002,11101,12001,30001,100021,100102,100201,101011, 110002,110101,111001}. Is this subsequence infinite? - _Zak Seidov_, Jul 07 2015
%H Zak Seidov, <a href="/A118688/b118688.txt">Table of n, a(n) for n = 1..10000</a>
%e 55 is in the sequence because (1) it is a semiprime and (2) the sum of its digits 5+5=10 is also a semiprime.
%p select(t -> map(numtheory:-bigomega,[t,convert(convert(t,base,10),`+`)])=[2,2], [$1..1000]); # _Robert Israel_, Jul 07 2015
%t Select[Range[514],PrimeOmega[{Total[IntegerDigits[#]],#}]=={2,2}&] (* _Zak Seidov_, Jul 07 2015 *)
%o (PARI) A007953(n)= { local(resul); resul=0; while(n>0, resul += n%10; n = (n-n%10)/10; ); return(resul); } { for(n=4,600, if( bigomega(n)==2, if(bigomega(A007953(n)) == 2, print1(n,","); ); ); ); } \\ _R. J. Mathar_, May 23 2006
%Y Cf. A001358, A007953.
%K base,nonn
%O 1,1
%A Luc Stevens (lms022(AT)yahoo.com), May 20 2006
%E Corrected by _R. J. Mathar_, May 23 2006
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