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2 4 4 − 1 = ( 2 4 2 + 1 ) ( 2 4 2 − 1 ) = ( 2 4 2 + 1 ) ( 2 4 + 1 ) ( 2 4 − 1 ) . We would show that 2 4 2 + 1 = 5 7 7 is a prime.
Note that it is not divisible by 3, 5, 7, 11, 13, 17, 19, or 23. Since 5 7 7 < 2 9 , we know now that it is a prime. Hence the answer is 5 7 7 .
We know that 577 is the largest possible prime since the other 2 factors, 25 and 23 are both less than 577.
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There wasn't a need to factor 2 4 2 − 1 (though I'd admit it's simple, since 2 4 2 + 1 > 2 4 2 − 1 , so 577 must be the largest prime.
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But what if 5 7 7 wasn't a prime??? We couldn't be sure whether 2 4 2 + 1 is a prime or composite... If 5 7 7 wasn't a prime, we would need the other prime factors to continue... Prime factorization should make the solution more clear...
@ Calvin: Agreed. I think that in addition to that I should have done all the trial divisions by 3, 5, 7, 11, 13, 17, 19 and 23 to 577.
From a 2 - b 2 =( a + b )( a − b )
We know
2 4 4 - 1 4 = ( 2 4 2 + 1 2 ) ( 2 4 2 - 1 2 ) = ( 2 4 2 + 1 2 ) ( 2 4 + 1 ) ( 2 4 − 1 ) = 5 7 7 × 2 5 × 2 3
Hence, 577, 25 and 23 are factors of 2 4 4 - 1 4 ,and only 577 and 23 are prime factors, thus the largest prime factor is 577
2 4 4 − 1 = ( 2 4 2 + 1 ) ( 2 4 2 − 1 ) = ( 5 7 7 ) ( 2 4 + 1 ) ( 2 4 − 1 ) = ( 5 7 7 ) ( 5 2 ) ( 2 3 )
Here is the equation, 5 7 7 is the largest prime, thus it is our answer.
You should verify that 577 is indeed prime.
= 2 4 4 − 1
= ( 2 4 2 + 1 ) ( 2 4 2 − 1 )
= ( 2 4 2 + 1 ) ( 2 4 + 1 ) ( 2 4 − 1 )
= ( 5 7 7 ) . ( 2 5 ) . ( 2 3 )
Since 577 is prime, so the largest prime factor is 577
By repeatedly applying the difference of squares we can see that 2 4 4 − 1 = ( 2 4 2 − 1 ) ( 2 4 2 + 1 ) = 2 3 × 2 5 × 5 7 7 . We need to factor 5 7 7 and see that if we test all of the primes up to the floor of the square root of 5 7 7 we get that 5 7 7 is prime. Thus, 5 7 7 is our answer.
Se Repararmos Isto é um Quadrado da Soma Pela Diferença :
(24^2+1) \times (24^2-1) (24^2+1) \times (24 +1) \times (24-1) (577) \times (5^2) \times (23)
Assim Temos o Maior Primo = 577
let 24=x
x^4-1=(x^2+1)(x^2-1) =(x^2+1)(x+1)(x-1) =(24^2+1)(24+1)(24-1) =(577)(25)(23)
because 577 is prime number,so,the largest prime factor of 24^4-1 is 577
24^4 - 1 = 331776 - 1 = 331775.
the prime factorization of 331775 = 5^2 . 23 . 577.
then the largest prime factor of 24^4 - 1 = 577
wonderfull solution: http://www.mathwarehouse.com/arithmetic/numbers/prime-number/prime-factorization-calculator.php
Factorize, check whether 5 7 7 is a prime (by taking its square root and dividing with prime numbers less than its square root) .
24^4-1= (24^2+1)(24^2-1). The greater prime factor is 24^2+1= 577.
Since 24^4 = 576^2, so (576^2)-1 = 575*577. Thus 577 is the largest prime factor of (24^4)-1.
24^4 - 1 can be written as (24 ^ 2 - 1) (24 ^ 2 + 1) which can be further broken down as (23) * (25) * (577).
24^4 - 1
= (24^2 - 1) * (24^2 + 1)
= (24 - 1) * (24 + 1) * (24^2 + 1)
= 23 * 5^2 * 577
Where the grates prime factor is 577.
24^4-1=331776-1=331775=5×66355=5×5×13271=5×5×23×577
or, 24^4-1=24^4-1^4=(24^2+1^2)×(24^2-1^2)=(24^2+1^2)×(24-1)×(24+1)=577×23×25=577×23×5×5
so, 577 is the largest prime factor of 24^4-1
again: http://www.mathwarehouse.com/arithmetic/numbers/prime-number/prime-factorization-calculator.php
2 4 4 − 1 = 5 2 ⋅ 5 7 7 ⋅ 2 3
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2 4 4 − 1
= ( 2 4 2 ) 2 − 1 2
= ( 2 4 2 + 1 ) ( 2 4 2 − 1 )
= ( 2 4 2 + 1 ) ( 2 4 + 1 ) ( 2 4 − 1 )
= 5 7 7 × 2 5 × 2 3
= 5 2 × 2 3 × 5 7 7
We can see that ⌊ 5 7 7 ⌋ = 2 4
Diving 577 by every prime below 24...
We can find that 577 is a prime
Hence, the largest prime is 5 7 7