Ta(2)

How many ordered pairs of positive integers ( a , b ) (a,b) are there such that a 3 + b 3 = 1729 a^{3} + b^{3} = 1729 ?

Hint : Taxicab

\infty 6 2 4

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1 solution

Tan Li Xuan
Apr 30, 2014

1729 is the second taxicab number(1729 is also known as the Hardy-Ramanujan number) ,which means that it can be written as the sum of two cubes in two distinct ways.However,the problem states "ordered pairs of integers",so there are 4 pairs.They are ( 9 , 10 ) , ( 10 , 9 ) , ( 12 , 1 ) , ( 1 , 12 ) (9,10),(10,9),(12,1),(1,12) .

Tricked :(

Krishna Ar - 6 years, 10 months ago

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You didn't see "ordered pairs" right?

Tan Li Xuan - 6 years, 10 months ago

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I didnt see that :(......

Krishna Ar - 6 years, 10 months ago

How? Actually, I gained some knowledge about taxicab numbers. How can we figure out the nth taxicab number and vice-versa? Also, why are they called taxicab numbers?

Kartik Sharma - 6 years, 10 months ago

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Just trivia, I guess.

The story of why they are called taxicab numbers is long. I trust a Google search will do it justice.

Daniel Liu - 6 years, 6 months ago

Oh! I didn't notice that it was the second taxicab number!!

Anik Mandal - 6 years, 10 months ago

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