Euler工程，找最长的数列！

定义一个正整数数列，其迭代公式为：

n = n/2 (当n为偶数)

n = 3n+1 (当n为奇数)

比如从n=13开始，计算这个数列得：

13 ->40->20->10->5->16->8->4->1

这个数列一共有10项。

要求在小于1百万的所有起始数中，哪个数能产生最长的数列。

-Euler project, find the longest series! Define a positive integers, the iterative formula: n = n/2 (when n is even) n = 3n+1 (when n is odd), n = 13 for example, from the beginning, this series was calculated: 13->　40->　20->　10->　5->　16->　8->　4->　1 this series a total of 10 items. Requires less than 1 million threshold in all, which few can produce the longest series.