2017201 7 2 20172017^2

2017201 7 2 + b 2 = c 2 20172017^2 + b^2 = c^2

How many positive integer solutions ( b , c ) (b,c) exist for this equation?


The answer is 13.

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1 solution

Miles Koumouris
Dec 8, 2017

Note that 2017201 7 2 = 7 3 2 × 13 7 2 × 201 7 2 20172017^2=73^2\times 137^2\times 2017^2 , and hence 2017201 7 2 20172017^2 has ( 2 + 1 ) ( 2 + 1 ) ( 2 + 1 ) = 27 (2+1)(2+1)(2+1)=27 positive factors. Also, ( c b ) ( c + b ) = 2017201 7 2 , (c-b)(c+b)=20172017^2, and so we are looking for two positive factors ( c b ) (c-b) and ( c + b ) (c+b) whose product is 2017201 7 2 20172017^2 . There are 27 27 ways to assign these factors, but 13 13 will give b b negative, and one will give b = 0 b=0 (when ( c b ) = ( c + b ) = 20172017 (c-b)=(c+b)=20172017 ). This leaves 13 13 ways to assign the factors so that b b and c c are positive, meaning there are 13 \boxed{13} positive, integral solutions for ( b , c ) (b,c) .

Why is this even a Level-5? It's not that hard of a problem. Plus, this really should be categorized under Number Theory vs Algebra......my two-cents.

tom engelsman - 3 years, 6 months ago

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