Seeking a mathematical equation! (Block Reward Halving)

[Gleb Gamow]

I'm looking an equation to plug in variables to calculate the following.

Depict the total supply of X coins to be accomplished in Y years, halving in Z days/years.

Example:

Total Supply: 100M coins
Block Target: 5 minutes
Block Reward: 100 coins
Block Reward Halves in: ? (days/years)
Total years till last block is hashed: 20 years
Premine: 0

The halving aspect is what I'm having trouble calculating and assume(?) the equation I'm requesting may incorporate the sigma symbol. Once I have the equation, I'll know how to use it.

To be clear, I'm seeking the formula to calculate the exact interval halving time frame to mine X coins in Y years with block target of M minutes and block reward of C coins.

Thanks in advance, all.