Question

Last digit in $2^{2^n}+1,n\in N,n\ne 1$ is

• A. $7$
• B. $3$
• C. $5$
• D. $1$

Answer 1

Answer: (A), (C)

The correct options are
A $7$
C $5$

$2^{2^n}+1$

$=(4{)}^n+1$

The last digit of $4^n$ can be either $4$ or $6$.

Since, $1$ is added to the number, the last digit of the number is also increased by $1$.

Hence, the last digit of $4^n+1$ can be either $5$ or $7$

Last digit of $2^{2^n}+1,n\in N,n\ne 1$ is $5$ or $7$.