5271736domain: NAppears in sequencesa(n) is the next number after a(n-1) which cannot be represented in the form 2*a(i) and Sum_{j=1..n-1} b_j*a(j) where 0 < i < n, b_j = 1 or 0. The sequence starts: a(1) = 1; a(2) = 2; a(3) = 3; a(4) = 5.at n=27A331811