Formula to identify common accounts if occurring within set timeframe

[eagerexceler]

Hello,

I have a large set of data (300k rows with unique account numbers) that in some instances also share a common identifying number. I want to identify accounts that share the common account identifier in cell C4 only if the date in cell d4 occurs less 30 days of a date in column D with the common account identifier in column C. Basically I need to identify if an account with this common identifier has another account with the same account identifier AND occurring in less than 30 days from each other.

Hope I didn't make this explanation too convoluted!

Thanks,