%N A001045 Jacobsthal sequence (or Jacobsthal numbers): a(n) = a(n-1) + 2a(n-2), with a(0) = 0, a(1) = 1. has a comment %C A001045 General form: k=2^n-k. [From .........., Dec 11 2008] Can someone (the author?) please explain what this means? Klaus Brockhaus