A problem by Anwar Alzhrani
Level
pending
How many numbers less than 10000 so that the product of its digit equal to 210
The answer is 54.
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1 solution
210=2×3×5×7
So that we can writ factors in 3 way
{2,3,5,7} >>> 4!=24
{6,5,7} >>> 3!=6
{6,5,7,1} >>> 4!=24
24+6+24=54