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Highest power of 2 that divides n.

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Never mind I messed up.
n=sym('94315998522576010519588224930693232398146802027362761139521');
a=7;
i=1;%this is a counter that starts from 1.
for i=1:inf
remainder=mod(n-1,2^i);
if remainder~=0
break
end
end
r=i-1%r takes the second last value of i because 2 raised to the last value is not divisible by n-1
s=rdivide(n-1,2^r)%this is the integer we get after n-1 is divided by the 2^(i-1)

  2 Comments

David Hill
David Hill on 9 Dec 2019
I am very confused. If you factor n-1, you get:
[ 2, 2, 2, 2, 2, 2, 3, 3, 3, 5, 13, 64763, 36377857, 478202419, 745336575801888629040192801767759];
How is a power of two ever going to be divisible by n-1? I obviously don't understand what you are trying to do.
Yuechuan Chen
Yuechuan Chen on 9 Dec 2019
Yeah I noticed what I did was very wrong. I was basically trying to set up a loop so that n-1 divides 2 repeatedly until the remainer is not 0.
I tried doing this
while mod(n-1,sym(2)^i)==0
i=i+1;
end
which also didn't get me anywhere cloe to the correct answer.
How would i get around this question? Thanks!

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Accepted Answer

James Tursa
James Tursa on 9 Dec 2019
Edited: James Tursa on 9 Dec 2019
In addition to David's comments, you need to do all of the calculations symbolically, so all of these should be sym: 2, i, r.

  1 Comment

Yuechuan Chen
Yuechuan Chen on 9 Dec 2019
Oh I see, thank you. that why it gave me some stupid numbers. I'm trying to find a way to divide n-1 by 2 repeatedly until the remainder isn't 0 and output how many times it has iterated which would be the answer I want, but I've been trying out all sorts of stuff but it didn't quite work out.

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More Answers (1)

Yuechuan Chen
Yuechuan Chen on 9 Dec 2019
n=sym('94315998522576010519588224930693232398146802027362761139521');
a=7;
i=1;
while mod(n-1,2^i)==0
i=i+1;
end
i
r=i-1%r takes the second last value of i because 2 raised to the last value is not divisible by n-1
s=vpa((n-1)/2^r)
Nevermind I think I've got it, My question was very unclear very sorry about that.

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