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What are the last 10 digits of 1666 6 3 + 5000 0 3 + 3333 3 3 16666^3 + 50000^3 + 33333^3 ?

Bonus: Can you generalize and prove it?


The answer is 5000033333.

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1 solution

Gabe Smith
Feb 14, 2016

Wow! The entire number is 166665000033333 , 166665000033333, how surprising... so the last 10 digits are 5000033333. 5000033333.

I'm not sure why this occurs and would love to know. Does anyone have a great solution? I'm guessing it has something to do with the fact that x + y + z = 100000 1 x+y+z = 100000 - 1 and maybe the factorization x 3 + y 3 + z 3 = ( x + y + z ) ( x 2 + y 2 + z 2 x y y z z x ) + 3 x y z . x^3+y^3+z^3 = (x+y+z)(x^2+y^2+z^2-xy-yz-zx) + 3xyz.

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