Wow, lots on angry kids on here raging at you for no reason.
This may seem crazy, but I tried my best to understand your question before responding.... I agree; I do not believe bungie is using a regular random number generator for drops. I'm willing to bet they have included modifiers to the formula. Even one completely undermines the legitimacy of a "RNG", and we can see examples of them doing so throughout the game. Unfortunately if this is true, they will never admit to it and it would be very difficult to test.
It can easily be proven that Bungie doesn't use a straight RNG algorithm.
Just Google "random number generator" , set the parameters, hit generate every time you turn in a focused Engram.