MCKapur
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 Sep 13 awarded Nice Question Sep 13 comment Show that 2n “1” digits subtract n “2” digits is a perfect square. @celtschk Ah, okay. Yep. I understand. Sep 13 comment Show that 2n “1” digits subtract n “2” digits is a perfect square. @leemes Right, but we haven't shown that 10^{n} - 1 is perfectly divisible by 3. Sep 13 accepted Show that 2n “1” digits subtract n “2” digits is a perfect square. Sep 13 comment Show that 2n “1” digits subtract n “2” digits is a perfect square. Awesome! Then I should be able to prove by induction that $10^{n} - 1$ is divisible by 3. Thanks! (will accept your answer in 8 mins... sorry, don't have much rep over here on the Math version of Stack Overflow :p) Sep 13 revised Show that 2n “1” digits subtract n “2” digits is a perfect square. edited body Sep 13 asked Show that 2n “1” digits subtract n “2” digits is a perfect square. Nov 4 awarded Popular Question Mar 25 awarded Autobiographer May 17 awarded Scholar May 17 comment Can somebody simply explain Wilson's theorem (for a 13 year old) thank you this is a very valuable answer... May 17 accepted Can somebody simply explain Wilson's theorem (for a 13 year old) May 17 revised Can somebody simply explain Wilson's theorem (for a 13 year old) deleted 3 characters in body May 17 comment Can somebody simply explain Wilson's theorem (for a 13 year old) Ok, Im still kind of stuck. If n is 4, (4-1)! would be 6. 6/1 works, 6/2 works, 6/3 works, but 6/4 doesn't work.... but 4 isn't prime.... and for if n was 5, (5-1)! would be 24. 24/1 works, 24/2 works, 24/3 works, 24/4 works, 24/5 however doesn't work... and that is prime... So I'm a bit muddled up May 17 awarded Supporter May 17 awarded Student May 17 awarded Editor May 17 revised Can somebody simply explain Wilson's theorem (for a 13 year old) added 226 characters in body May 17 comment Can somebody simply explain Wilson's theorem (for a 13 year old) ok ill try that, but can you answer my question please? May 17 comment Can somebody simply explain Wilson's theorem (for a 13 year old) can you answer my previous question? yes, i read that. I understand what it means, just not how it applies to this situation and how it can help prove whether a number is prime or not – Rohan Kapur 18 mins ago