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Question Number 27888 by Rasheed.Sindhi last updated on 16/Jan/18

 a and b are distinct primes and  x,y∈{0,1,2,...}.  What is the number of divisors  common to the numbers (a^x b^y )  and (a^y b^x )?

$$\:\mathrm{a}\:\mathrm{and}\:\mathrm{b}\:\mathrm{are}\:\boldsymbol{\mathrm{distinct}}\:\boldsymbol{\mathrm{primes}}\:\mathrm{and} \\ $$$$\mathrm{x},\mathrm{y}\in\left\{\mathrm{0},\mathrm{1},\mathrm{2},...\right\}. \\ $$$$\mathrm{What}\:\mathrm{is}\:\mathrm{the}\:\boldsymbol{\mathrm{number}}\:\boldsymbol{\mathrm{of}}\:\boldsymbol{\mathrm{divisors}} \\ $$$$\boldsymbol{\mathrm{common}}\:\mathrm{to}\:\mathrm{the}\:\boldsymbol{\mathrm{numbers}}\:\left(\boldsymbol{\mathrm{a}}^{\boldsymbol{\mathrm{x}}} \boldsymbol{\mathrm{b}}^{\boldsymbol{\mathrm{y}}} \right) \\ $$$$\boldsymbol{\mathrm{and}}\:\left(\boldsymbol{\mathrm{a}}^{\boldsymbol{\mathrm{y}}} \boldsymbol{\mathrm{b}}^{\boldsymbol{\mathrm{x}}} \right)? \\ $$

Commented by prakash jain last updated on 16/Jan/18

2^(min(x,y)+1)

$$\mathrm{2}^{\mathrm{min}\left({x},\mathrm{y}\right)+\mathrm{1}} \\ $$

Commented by Rasheed.Sindhi last updated on 16/Jan/18

Thanks Sir! Any process?  Why 2 is involved?

$$\mathrm{Than}\Bbbk\mathrm{s}\:\mathrm{Sir}!\:\mathrm{Any}\:\mathrm{process}? \\ $$$$\mathrm{Why}\:\mathrm{2}\:\mathrm{is}\:\mathrm{involved}? \\ $$

Commented by Rasheed.Sindhi last updated on 17/Jan/18

Ok Sir!

$$\mathrm{Ok}\:\mathrm{Sir}! \\ $$

Commented by prakash jain last updated on 17/Jan/18

2^(min(x,y)+1)  is wrong it should  have been (min(x,y)+1)^2 .

$$\mathrm{2}^{\mathrm{min}\left(\mathrm{x},\mathrm{y}\right)+\mathrm{1}} \:\mathrm{is}\:\mathrm{wrong}\:\mathrm{it}\:\mathrm{should} \\ $$$$\mathrm{have}\:\mathrm{been}\:\left(\mathrm{min}\left(\mathrm{x},\mathrm{y}\right)+\mathrm{1}\right)^{\mathrm{2}} . \\ $$

Answered by mrW2 last updated on 17/Jan/18

Commented by Rasheed.Sindhi last updated on 17/Jan/18

Quite Ok Sir! THANKS-a-LOT!

$$\mathrm{Quite}\:\boldsymbol{\mathrm{Ok}}\:\mathrm{Sir}!\:\mathcal{THANKS}-{a}-\mathcal{LOT}! \\ $$

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