MHB Solving for $(a,\,b,\,c)$ with Powers of 2

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Find all positive integers $(a,\,b,\,c)$ such that $ab-c,\,bc-a,\,ca-b$ are all powers of 2.
 
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Let $a=b$. Then $a(c-1)$ and $a^2-c=2^n$ are powers of 2, hence, $a=2^k,\,c-1=2^m$. Considering equality $2^{2k}=a^2=1+(c-1)+(a^2-c)=1+2^m+2^n$ modulo 4, we get $(m, \,n)=(0,\,1)$, $k=1$. This leads to solutions $(2,\,2,\,2)$ and $(2,\,2,\,3)$.

Now, assume that $a<b<c$. Denote $bc-a=2^A,\,ac-b=2^B$, then $2^A-2^B=(c+1)(b-a)>0$ hence $A>B$ and $2^B$ divides $(c+1)(b-a)$. Also, $2^B$ divides $2^A+2^B=(c-1)(a+b)$. Either $c-1$ or $c+1$ is not divisible by 4, hence either $2(b-a)$ or $2(b+1)$ is divisible by $2^B$, in both cases we have $a+b\ge 2^{B-1}$. So, $a(b+1)\le ac=2^B+b\le 2(a+b)+b$, i.e. $ab\le a+3b<4b$. Hence, $a<4$.

If $a=2$, then $2^C=2b-c,\,2^B=2c-b>1$, hence $B>0$. We get $b=\dfrac{(2^{C+1}+2^B)}{3},\,c=\dfrac{(2^{B+1}+2^C)}{3}$. If $C\ge 1$ then both $b$ and $c$ are even, hence $bc-2$ is not divisible by 4, in this case, $bc-2\ge 3\cdot 4-2=10$ cannot be a power of 2.

If $C=0$, then by modulo 3 we see that $B$ is even and $bc-2=\dfrac{(2+2^B)(2^{B+1}+1)-18}{9}=\dfrac{2^{2B+1}+5\cdot2^B-16}{9}$ must be a power of 2. This is not possible if $B\ge 6$, since 32 does not divide numerator $2^{2B+1}+5\cdot 2^B-16$ and it is greater than $16\cdot 9$. For $B=2$, we get $b=a=2$ and for $B=4$, we get $b=6$ and $c=11$.

If $a=3$, then $2^C=3b-c,\,2^B=3c-b\ge 2c+1>4$, hence $B\ge 3$. We get $b=\dfrac{(3\cdot 2^{C}+2^B)}{8},\,c=\dfrac{(3\cdot 2^{B}+2^C)}{8}$. We get $B>C$ (from $b<c$) and since $B\ge 3$, we get that $C\ge 3$ as well and $2^A=bc-3=(3\cdot 2^{C-3}+2^{B-3})(3\cdot 2^{B-3}+2^{C-3})-3$. If $B>C>3$, this is odd and greater than 1, hence they are not power of 2.

If $C=3$ we get $2^A=2^{B-3}(10+3\cdot2^{B-3})$. This is a power of 2 if and only if $B-3=1 \implies B=4$, $b=5,\,c=7$.

Hence, $(a,\,b,\,c)=(2,\, 2,\, 2),\,(2,\, 2,\, 3),\,(2,\, 6,\, 11),\,(3,\, 5,\, 7)$ and their permutations.
 
Here is a little puzzle from the book 100 Geometric Games by Pierre Berloquin. The side of a small square is one meter long and the side of a larger square one and a half meters long. One vertex of the large square is at the center of the small square. The side of the large square cuts two sides of the small square into one- third parts and two-thirds parts. What is the area where the squares overlap?

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