bell.cpp

给定正整数n

#include <iostream>
using namespace std;
__int64 a[20][20];

int main()
{
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);

	__int64 sum;
	int n, i, j;
	cin>>n;
	for(i=1;i<n+1;i++)
	{
		a[i][1] = 1;
		a[i][i] = 1;
		for(j=2;j<i;j++)
		{
			a[i][j] = j * a[i-1][j] + a[i-1][j-1];
		}
	}
	sum = 0;
	for(i=1;i<n+1;i++)
		sum += a[n][i];
	printf("%I64d\n",sum);
	return 0;
}