The number 27,000,001 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)(9x4−3x2+1)=(3x2+1)((9x4+6x2+1)−9x2)=(3x2+1)((3x2+1)2−(3x)2)=(3x2+1)(3x2+3x+1)(3x2−3x+1) Letting x=10, we get that 27000001=301⋅331⋅271. A quick check shows that 301=7⋅43, so that 27000001=7⋅43⋅271⋅331. Each factor here is prime, and their sum is 652.
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