Sequence S with the following properties: (i) a(1)=2; (ii) for n in S, a(n)=a(1)+a(2)+...+a(n-1); (iii) for n not in S, a(n)=the smallest number different from a(1), ..., a(n-1) not breaking property (ii).

A121175

Sequence S with the following properties: (i) a(1)=2; (ii) for n in S, a(n)=a(1)+a(2)+...+a(n-1); (iii) for n not in S, a(n)=the smallest number different from a(1), ..., a(n-1) not breaking property (ii).