"How did the "" _ + _ + _ = 30 using 1, 3, 5, 7, 9, 11, 13 and 15"" riddle become so popular?"
How many 6-digit numbers are there using the digits 0, 1, 2, 3, 4, 5, 6, 7, 8, and 9 if the first digit cannot be 0 but repeated digits are allowed?