MathDB
classic sequence

Source: baltic way, 2006

May 1, 2007

Problem Statement

For a sequence (an)n1(a_{n})_{n\geq 1} of real numbers it is known that an=an1+an+2a_{n}=a_{n-1}+a_{n+2} for n2n\geq 2. What is the largest number of its consecutive elements that can all be positive?