A072966 Numbers which are not the sum of two semiprimes.

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

Offset: 1

Author

Lior Manor, Aug 13 2002

Keywords

• nonn

Comments

Is this sequence finite?

See the graph of sequence A072931 for compelling evidence that 33 is the last term of this sequence. - T. D. Noe, Apr 11 2007

Examples

			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.
		

Crossrefs

Cf. A001358.

Programs

Mathematica

lim = 10000;
s = Select[Range[lim], PrimeOmega[#] == 2 &];
c = Map[Total,Union[Subsets[s, {2}], Table[{s[[i]], s[[i]]}, {i, 1, Length[s]}]]];
Join[Complement[Range[0, lim], c], ">", lim ](* Robert Price, Mar 30 2019 *)