Calculate the Sum up to nth term :

#include<stdio.h>
int main(void)
{
    int sum=0,i,n,d,a_n,a_1;
    a_1=1;
    d=10;

    printf("Enter the nth number:");
    scanf("  %d",&n);

    a_n=a_1+(n-1)*d;

    printf("The valude of a_n is:  %d\n",a_n);

    for(i=0; i<a_n; i=i+10)
    {
        sum=i+sum;
    }

    printf("Sum is: %d\n",sum);

    return 0;
}