To convert decimal number to binary format use base 2
Int32 Number = 15;
Console.WriteLine(Convert.ToString(Number, 2)); //OUTPUT : 1111
To convert decimal number to octal format use base 8
int Number = 15;
Console.WriteLine(Convert.ToString(Number, 8)); //OUTPUT : 17
To convert decimal number to hexadecimal format use base 16
var Number = 15;
Console.WriteLine(Convert.ToString(Number, 16)); //OUTPUT : f