Why is my Index was out of range in MVC 4? - asp.net-mvc-4

Question

I've tried to create some list with increase number after some calculation each month for a year.
For example, in month 1 number = 1, month 2 number = 3, month 3 number = 5.
The calculation is like this number[i] = i + number[i - 1]. Which i is the month.
I want to show all the list like this
Month[1] = 1,
Month[2] = 3,
Month[3] = 5,
Month[4] = 7,
Month[5] = 9,
Month[6] = 11,
Month[7] = 13,
...
Month[12] = 23
Here's my Controller
for (i = 1; i <= 12; i++)
{
List<int> number = new List<int>();
if (i <= 12)
{
number[i] = a(i, number[i - 1]);
}
else
{
//something else
}
}
Here's my a function
public int a(int month, int number)
{
try
{
a = month + number;
}
catch (Exception ex)
{
throw ex;
}
return a;
}
But, when executed i'm getting this error
Index was out of range. Must be non-negative and less than the size of the collection.
I've change the controller into this
for (i = 0; i <= 12; i++)
{
//...
}
But have the same error. Can someone help me? Why I'm getting this error?

Answer 1

Try this
Fiddle demo
int[] number = new int[13];
for (int i = 1; i <= 12; i++)
{
if (i <= 12)
{
number[i] = a(i, number[i - 1]);
}
else
{
//something else
}
}
int j = 1;
List<int> item = new List<int>();
foreach (var a in number)
{
if (j <= 12)
{
item.Add(a);
}
else
{
break;
}
j++;
}
public int a(int month, int number)
{
int a = 0;
try
{
a = month + number;
}
catch (Exception ex)
{
throw ex;
}
return a;
}