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What is the remainder when 44^(197) divided by 7?

Question

What is the remainder when 44^(197) divided by 7?

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Solution

To find the remainder when 44197 44^{197} is divided by 7, we can use modular arithmetic and properties of congruences.

Step 1: Simplify the base modulo 7. 4444mod7 44 \equiv 44 \mod 7 44=7×6+2 44 = 7 \times 6 + 2 442mod7 44 \equiv 2 \mod 7

So, 441972197mod7 44^{197} \equiv 2^{197} \mod 7 .

Step 2: Use Fermat's Little Theorem, which states that if p p is a prime number and a a is an integer not divisible by p p , then ap11modp a^{p-1} \equiv 1 \mod p .

Here, p=7 p = 7 and a=2 a = 2 . According to Fermat's Little Theorem: 261mod7 2^{6} \equiv 1 \mod 7

Step 3: Express 197 in terms of multiples of 6. 197=6×32+5 197 = 6 \times 32 + 5

So, 2197=26×32+5=(26)32×25 2^{197} = 2^{6 \times 32 + 5} = (2^6)^{32} \times 2^5

Using Fermat's Little Theorem: (26)321321mod7 (2^6)^{32} \equiv 1^{32} \equiv 1 \mod 7

Therefore, 21971×25mod7 2^{197} \equiv 1 \times 2^5 \mod 7 219725mod7 2^{197} \equiv 2^5 \mod 7

Step 4: Calculate 25mod7 2^5 \mod 7 . 25=32 2^5 = 32 3232mod7 32 \equiv 32 \mod 7 32=7×4+4 32 = 7 \times 4 + 4 324mod7 32 \equiv 4 \mod 7

So, the remainder when 44197 44^{197} is divided by 7 is 4 \boxed{4} .

This problem has been solved

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