Given a set of 1 × 2 dominoes, how many different ways are there to tile and 2 × n rectangle placing a single domino vertically (2 × 1) or stacking two dominoes horizontally? for example, for n=3,

Given a set of 1 × 2 dominoes, how many different ways are there to tile and 2 × n rectangle placing a single domino vertically (2 × 1) or stacking two dominoes horizontally? for example, for n=3, there are 3 ways.