Divisors’ powers

Let n n be a positive integer with at least 4 divisors and 1 = d 1 < d 2 < d 3 < < d k = n 1=d_1<d_2<d_3<…<d_k=n all its positive divisors. Find the sum of all possible values of n n such that: n = d 2 2 + d 4 4 + 2 n=d_2^2+d_4^4+2


The answer is 1302.

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1 solution

Emanuele Prati
Apr 17, 2019

First of all, if n n is odd the LHS will be odd and, because all the divisors of an odd number are odd too, and so their powers, the RHS will be the sum of two odds and a even so will be even; this is a nonsense. So n n must be even, so d 2 d_2 must be equal 2, so n = 2 2 + d 4 4 + 2 = d 4 4 + 6 n=2^2+d_4^4+2=d_4^4+6 . Since d 4 d_4 divides n n and d 4 4 d_4^4 , it must divide 6 too; it can’t be equal 3, otherwise 2 < d 3 < 3 2<d_3<3 , so it must be equal 6; in conclusion n = 6 4 + 6 = 1302 n=6^4+6=1302 . It can be simply verified that 4 doesn’t divide 1302 so d 2 = 2 d_2=2 , d 3 = 3 d_3=3 and d 4 = 6 d_4=6

Brilliant Bro

Uttam Manher - 2 years, 1 month ago

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