Published by:
CGP EDU Academic Team
Published on: August 11, 2026
Let a n = 
, then
Text Solution
Verified by ExpertsThe correct answer is:
CHECK THE SOLUTION.
(a, b, c, d)
As a 912 , a 951 and a 480 are divisible by 3, none of them is prime. For a 91 , we have
a 91 = 
= 
(10 91 – 1)
= 
[(10 7 ) 13 – 1]
= 
= [(10 7 ) 12 + (10 7 ) 11 + ….+ 10 7 + 1]
× [10 6 + 10 5 + ….. + 10 + 1]
= a 91 is not prime.
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