1,3

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

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

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.

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 *)

Cf. A001358.

Sequence in context: A005577 A263362 A336733 * A245761 A059759 A042952

Adjacent sequences: A072963 A072964 A072965 * A072967 A072968 A072969

nonn

Lior Manor Aug 13 2002

approved