using System;

public class Program

{

    public static void Main()

    {

        DateTime? date = new DateTime(2021,2,7);

var courseId = 185310;

var partitionKey = String.Format("ReportEntityByTimestampCourse_{0:d8}_{1:d19}", courseId, DateTime.MaxValue.Ticks - (date ?? DateTime.UtcNow).Date.Ticks);

​

//partitionKey.Dump();

​

Console.WriteLine(partitionKey);

    }

}