给定一个1~n之间的数，问由连续素数凑成该数的的方案有几种，比如：53 = 53， 53 = 5 + 7 + 11 + 13 + 17，那么方案数就是2.
This problem is based on an exercise of David Hilbert, who pedagogically suggested that one study the theory of 4n+1...
Given a positive integer X, an X-factor chain of length m is a sequence of integers,
1 = X0, X1, X2, …, Xm = X...
Write a program which reads an integer n and prints the number of prime numbers which are less than or equal to n. A...