题目

Charlton Heston, the Hollywood actor who has played such roles as Ben Hur and Moses, was once asked if it was destiny that got him where he is today. Heston replied that destiny should be discounted(不可全信). To him, his success was due to knowing what he wanted, having a bit of luck and working hard. He summed up his attitudes to life and achievements: “Never give up! Never give up!” In every important aspect of our life, never giving up is the right approach. Never give up believing in yourself and what you can do for yourself and other. Never give up trying to make your ca 如图所示四个图形中，着色三角形的个数依次构成一个数列的前4项，则这个数列的一个通项公式为________．