x a + x b + x c + x d + x e = 1 9 6 0 7
If a , b , c , d , e and x are positive integers satisfying the equation above, find a + b + c + d + e + x .
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The factors of 1 9 6 0 7 are 1 , 7 , 2 8 0 1 , and 1 9 6 0 7 , where 7 and 2 8 0 1 are primes. It is obvious that x = 1 and x = 1 9 6 0 7 and since 2 8 0 1 2 > 1 9 6 0 7 and 2 8 0 1 1 + 2 8 0 1 1 + 2 8 0 1 1 + 2 8 0 1 1 + 2 8 0 1 1 < 1 9 6 0 7 , x = 2 8 0 1 , thus we must have x = 7 .
Assuming that a ≤ b ≤ c ≤ d ≤ e and that a = 1 so that:
x a + x b + x c + x d + x e = 7 ( 1 + 7 b − 1 + 7 c − 1 + 7 d − 1 + 7 e − 1 ) = 7 ( 2 8 0 1 )
Assuming that 1 + 7 b − 1 + 7 c − 1 + 7 d − 1 + 7 e − 1 is a geometric progression sum with common ratio 7 , then:
k = 0 ∑ 4 7 k = 7 − 1 7 5 − 1 = 6 1 6 8 0 6 = 2 8 0 1 , which is true.
Then we have a = 1 , b = 2 , c = 3 , d = 4 , e = 5 and x = 1 and that a + b + c + d + e + x = 1 + 2 + 3 + 4 + 5 + 7 = 2 2 .