Problem 2910. Mersenne Primes vs. All Primes

Created by goc3

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315 Solutions
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Last Solution submitted on Aug 06, 2020

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1 Comment

Jean-Marie Sainthillier on 16 May 2019

Hello Grant,
I don't know if it's a lot of work but it could be a good idea to add a Prime Numbers group 2 with more difficult problems. I think about beautiful Ned's problems (primes ladders, Longest prime diagonal, Twins in a window ...).

Solution Comments

Solution 571313

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Anupam Agarwal on 1 Feb 2015

My logic is right but test cases are very hude numbers.... failed to evaluate...

Guillaume on 2 Feb 2015

You need to learn to avoid loops. You can use isprime on an array. In any case, your logic is wrong. You never test that b is prime.

goc3 on 2 Feb 2015

As Guillaume pointed out, this solution doesn't test if the numbers in b are Mersenne primes, simply if they're less than 2^n-1, which is not the right criterion. Further, you concatenate the index of the loop (j, which goes from 1 to 1...), rather than a Mersenne prime to b.

Also, this problem is designed, as many of James's problems are, to fail by timeout unless vectorized solutions are used.

Anupam Agarwal on 3 Feb 2015

i have corrected the logic but plz can u tell me smthing about vectorized solutions...
u can also mail me on anupamagarw@gmail.com

Jan Orwat on 3 Feb 2015

http://nl.mathworks.com/help/matlab/matlab_prog/vectorization.html

Jan Orwat on 3 Feb 2015

some tips: http://nl.mathworks.com/help/matlab/matlab_prog/techniques-for-improving-performance.html

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