Let P be a prime number such that the number P² + 11 has exactly 6 positive divisors. Find P.
Answers
P may be 3
Step-by-step explanation:
As 9+11=20 has 6 positive divisors:1,2,4,5,10 and 20
Given : 'p' be a prime number such that the number p²+11 has exactly 6 positive divisors
To Find : value of p
Solution:
p = 2 => p² + 11 = 15 ahs 4 divisors ( 1 , 3 , 5 , 15)
p =3 => p² + 11 = 20 has 6 exactly divisors ( 1 , 2 , 4 , 5 , 10 , 20 )
Hence p = 3
after that all prime can be written in form :
p = 6q - 1 , 6q + 1
p² + 11 = (6q - 1)² + 11 = 36q² + 1 - 12q + 11 = 36q² - 12q + 12
= 12( 3q² - q + 1)
12 it self has 6 divisors Hence more than 6 divisors
p² + 11 = (6q+ 1)² + 11 = 36q² + 1 + 12q + 11 = 36q² + 12q + 12
= 12( 3q² + q + 1)
12 it self has 6 divisors Hence more than 6 divisors
so only possible p = 3
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