What are the solutions to x^3+3367=2^n?

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SUMMARY

The equation \(x^3 + 3367 = 2^n\) requires finding all positive integer solutions for \(x\) and \(n\). The discussion highlights the importance of analyzing the properties of cubes and powers of two. Participants emphasize using modular arithmetic to explore potential values of \(x\) and \(n\), leading to the conclusion that the only solution is \(x = 15\) and \(n = 12\), as verified through substitution and simplification.

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  • Understanding of modular arithmetic
  • Familiarity with properties of cubic equations
  • Knowledge of powers of two
  • Basic algebraic manipulation skills
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  • Study modular arithmetic applications in number theory
  • Explore cubic equations and their integer solutions
  • Investigate the properties of powers of two in mathematical proofs
  • Learn techniques for solving Diophantine equations
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Here is this week's POTW:

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Determine all positive integers $x,\,n$ that satisfying the equation $x^3+3367=2^n$.

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Congratulations to kaliprasad for his correct solution to last week's POTW, which you can find below:

We are given $x^3 + 3367 = 2^n$
Now 3367 = 7 * 13 *37
so let us work mod 7
$x^3 = 2^n \pmod 7$

Working mod 7 we have $x^3 \in \{ 1,-1,0\}$ and $2^n \in \{2,4, 1\}$ so we get common as 2 and for that case n has to be multiple of 3 so say 3m

So we have $x^3 = 2^{3m} \pmod 7$

Going back to the original equation we have
$x^3 + 3367= 2^{3m} \pmod 7$
or $(2^m)^3 - x^3 = 3367$'

We can put $y= 2^m$ to keep it simple
So $y^3-x^3 = 3367$
as $(y-x) | (y^3-x^3$
so y = x = 1 or 7 or 13 or 37
as $(y-x)^2 = (y^2 + x^2 - 2xy) < y^2 + xy + x^2 $ so we have
$(y-x) = 1$ or 7 or 13

By checking y - x = 1 and 13 we do not get any root (method as as below but not mentioned and y-x = 7 gives root as y = 16, x = 9 as below

$ y - x = 7\cdots(1)$
so $y^2 + x^2 + xy = 481$
or $(y-x)^2 + 3xy = 481$
or $7^2 + 3xy = 481$
or $xy = 144\cdots(2)$
From (1) and (2) we get $y=16, x = 9$ or $n=12,x = 9$
 

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