Arghh......REmainders

The remainder when 456 6 1021 4566^{1021} is divided by 23 can be expressed in the form a a a^{a} . Find 100 a 100{a} .


The answer is 200.

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4 solutions

Jaiveer Shekhawat
Oct 27, 2014

Well I will go for an explicit solution...

We know that according to fermat's little remainder theorem:

a p 1 a^{p-1} 1 \equiv1 (mod p)

456 6 22 4566^{22} 1 \equiv1 (mod 23)

456 6 22 ( 46 ) 4566^{22(46)} 1 \equiv1 (mod 23)

456 6 1012 4566^{1012} 1 \equiv1 (mod 23)

Now we have 456 6 9 4566^{9} remaining with us...

4566= 2 × 3 × 761 2 \times3 \times761

761 2 \equiv2 (mod 23)

456 6 9 4566^{9} \equiv\(2^{9} . 3 9 3^{9} . 76 1 9 761^{9} ) (mod 23)

456 6 9 4566^{9} \equiv\(2^{9} . 3 9 3^{9} . 2 9 2^{9} ) (mod 23)

456 6 9 4566^{9} \equiv\(12^{9} ) (mod 23)

thus we need to find y where

1 2 9 12^{9} y \equiv y (mod23)

12 12 \equiv 12 (mod23)

1 2 2 12^{2} 6 \equiv 6 (mod23)

1 2 3 12^{3} 3 \equiv 3 (mod23)

1 2 3 12^{3} X 1 2 3 12^{3} X 1 2 3 12^{3} 3 X 3 X 3 \equiv 3 X 3 X 3 (mod23)

= 1 2 9 12^{9} 27 \equiv 27 (mod23)

= 1 2 9 12^{9} 4 \equiv 4 (mod23)

Therefore,

456 6 1021 4566^{1021} 4 \equiv 4 (mod23)

4 = 2 2 2^{2}

Implies that a=2

therefore, 100a= 200 \huge{200}

Maybe there is no need for such hard calculations......

Bryan Lee Shi Yang - 6 years, 3 months ago

How have you written this line .Please explain 456 6 9 4566^{9} \equiv\(2^{9} . 3 9 3^{9} . 76 1 9 761^{9} ) (mod 23)

Chirayu Bhardwaj - 5 years, 2 months ago
Trí Onii-sama
Oct 21, 2014

I just guess, a^a<23 so a is 1 or 2

Cool. ..................

Krishna Ar - 6 years, 7 months ago

Exactly what I did!

Pranjal Jain - 6 years, 7 months ago

same here....

abhishek anand - 6 years, 5 months ago

I did that and tried first with 2 :P

Mahtab Hossain - 6 years ago

a^a cannot be bigger than 23.

Ankit Kumar Jain
Mar 21, 2015

a a a^{a} < 23. So either 1 or 2.

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