A072966 Numbers which are not the sum of two semiprimes.

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

Offset

1,3

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

Links

Table of n, a(n) for n=1..13.

Example

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.

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 *)

Crossrefs

Cf. A001358.

Sequence in context: A005577 A263362 A336733 * A363246 A245761 A371248

Adjacent sequences: A072963 A072964 A072965 * A072967 A072968 A072969

Keyword

nonn

Author

Lior Manor, Aug 13 2002

Status

approved