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Old 08-28-2016, 10:12 AM
The Great Unwashed The Great Unwashed is offline
Join Date: Mar 2002
Location: France
Posts: 2,081
Originally Posted by Indistinguishable View Post

The challenge to you (after you are able to actually try out enough examples to assure yourself this does indeed work) is to explain: why does this work?

Isn't it perfectly obvious that (8221^((A(1+4995A+16616700A^2))mod1000)/2)-1)mod1000 = A ?

No. Please save me.