Value of pi using basel's equation

Problem statement 

Write a c program to calculate the value of pi*pi/6 using Basel's equation

the equation is pi²/6=1/1²+1/2²+1/3² and so on  

#include<stdio.h>
float pi( float i);
int main()
{ 
  float y,i;
  i=1.0;
  y=pi(i);
  printf("the value of pi*pi/6 is %f",y);
  return 0;
}

float pi(float i)
{
  float e,sum;
  e=1/(i*i);
  if(e<.000001)
    {
      return 0;
    }
  else
    {
      i++;
      sum=e+pi(i);
    }
  return sum;
}