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A072966 Numbers which are not the sum of two semiprimes. 9

%I

%S 0,1,2,3,4,5,6,7,9,11,17,22,33

%N Numbers which are not the sum of two semiprimes.

%C Is this sequence finite?

%C See the graph of sequence A072931 for compelling evidence that 33 is the last term of this sequence. - _T. D. Noe_, Apr 11 2007

%e a(10) = 11 since there is no way to represent 11 as a sum of two semiprimes. 13 is not a term since 13 = 4 + 9.

%t lim = 10000;

%t s = Select[Range[lim], PrimeOmega[#] == 2 &];

%t c = Map[Total,Union[Subsets[s, {2}], Table[{s[[i]], s[[i]]}, {i, 1, Length[s]}]]];

%t Join[Complement[Range[0, lim], c], ">", lim ](* _Robert Price_, Mar 30 2019 *)

%Y Cf. A001358.

%K nonn,more

%O 1,3

%A _Lior Manor_ Aug 13 2002

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Last modified April 24 16:16 EDT 2019. Contains 322430 sequences. (Running on oeis4.)