Program.cs

static unsafe void Fibonacci()
{
    const int arraySize = 20;
    int* fib = stackalloc int[arraySize];
    int* p = fib;
    *p++ = *p++ = 1;
    for (int i = 2; i < arraySize; ++i, ++p)
    {
        *p = p[-1] + p[-2];
    }
    for (int i = 0; i < arraySize; ++i)
    {
        Console.WriteLine(fib[i]);
    }
}