Maths Olympiad Prep

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Algebra Difficulty 5.0 AIME, harder Find the answer

The number 27,000,00127,000,001 has exactly four prime factors. Find their sum.

A number or a short expression. Spacing and $ signs are ignored.

Solution

First, we factor 27x6+1=(3x2)3+1=(3x2+1)(9x43x2+1)=(3x2+1)((9x4+6x2+1)9x2)=(3x2+1)((3x2+1)2(3x)2)=(3x2+1)(3x2+3x+1)(3x23x+1)\begin{aligned} 27 x^{6}+1 & =\left(3 x^{2}\right)^{3}+1 \\ & =\left(3 x^{2}+1\right)\left(9 x^{4}-3 x^{2}+1\right) \\ & =\left(3 x^{2}+1\right)\left(\left(9 x^{4}+6 x^{2}+1\right)-9 x^{2}\right) \\ & =\left(3 x^{2}+1\right)\left(\left(3 x^{2}+1\right)^{2}-(3 x)^{2}\right) \\ & =\left(3 x^{2}+1\right)\left(3 x^{2}+3 x+1\right)\left(3 x^{2}-3 x+1\right) \end{aligned} Letting x=10x=10, we get that 27000001=30133127127000001=301 \cdot 331 \cdot 271. A quick check shows that 301=743301=7 \cdot 43, so that 27000001=74327133127000001=7 \cdot 43 \cdot 271 \cdot 331. Each factor here is prime, and their sum is 652.

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