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2520 is the smallest number that can be divided by each of the numbers from 1 to 10 without any remainder.

What is the smallest positive number that is evenly divisible by all of the numbers from 1 to 20?

题目大意：

2520是最小的能被1-10中每个数字整除的正整数。

最小的能被1-20中每个数整除的正整数是多少？

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <math.h>

#define N 20

int gcd(int a, int b)
{
	if (b == 0)
		return a;
	else
		return gcd(b, a % b);
}

int lcm(int a, int b)
{
	return a / (gcd(a, b)) * b;
}

void solve()
{
	int i, s = 2;
	for (i = 3; i <= N; i++) {
		s = lcm(s, i);
	}
	printf("%d\n", s);
}

int main()
{
	solve();
	return 0;
}

 Answer:232792560
Completed on Tue, 2 Apr 2013, 07:21