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please guide me how to expand a number in the form of $3^x 7^y$ example:

$1 = 3^0 7^0$

$21 = 3^1 7^1$

i have tried by finding numbers which can be expressed in form of any one such as for only $3^x$ but cant find in the product form

Tori
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    Dived the nuber by $3$ until you cannot, then divide what you're left with by $7$ until you cannot anymore. If you're left with only $1$, then that number is not the product of a power of $7$ and a power of $3$. –  Feb 03 '19 at 07:16

1 Answers1

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You need to factorise the number into prime dividers. Then, look for the number of 3's and the number of 7's and that are the exponents of

3
x


7
y