奇怪的铸造行为。无法将对象（int）强制转换为long

I have the following code:

我有以下代码：

int intNumber1 = 100;
object intNumber2 = 100;
bool areNumberOfTheSameType = intNumber1.GetType() == intNumber2.GetType(); // TRUE
bool areEqual = intNumber1.Equals(intNumber2); // TRUE

long longNumber1 = (long) intNumber1; // OK
long longNumber2 = (long) intNumber2; // InvalidCastException. Why?
int intN