1. Write a program that takes an integer n and displays the value of $$U_n$$ respecting: 
   $$U_1=1$$ ;
   $$U_n=\sum_{i=1}^{n-1}\frac{U_i}{(i-1)!}$$ for n>2 ;
2. Write a program that asks the user to enter an integer a and then prints the series elements from $$U_1$$ to $$U_a$$.

#include<stdio.h>
int main()
{
	int n, i, j;
	int   fact=1;
	double u1,u2;
	u1=1;
	u2=0;
	do{
		printf("Enter n: ");
		scanf("%d",&n);
	}while(n<=0);

    	for(i=2;i<=n;i++)
    	{
        	u2 +=  u1/fact;
        	fact*= (i-1) ;
        	u1 = u2;
    	}
    	printf("U%d=%.4lf\n",n,u1);
	return 0;
}



#include<stdio.h>
int main()
{
	int n, i, j;
	int   fact=1;
	double u1,u2;
	u1=1;
	u2=0;
	
	do{
		printf("Enter n: ");
		scanf("%d",&n);
	}while(n<=0);

    	for(i=2;i<=n;i++)
    	{
        	u2 +=  u1/fact;
        	fact*= (i-1) ;
        	u1 = u2;
        	printf("U%d=%.4lf\n",i,u1);
    	} 
	return 0;
}