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Some Sum Cubes is the Multiple of a Cube (Posted on 2024-04-13) Difficulty: 3 of 5
Each of x, y and z is a positive integer with gcd(x,y,z)=1

Determine all possible pairs (x,y,z) satisfying this equation:

x3+y3=7z3 where x+y+z < 10^10

No Solution Yet Submitted by K Sengupta    
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Some Thoughts a solution | Comment 1 of 3
I did not check all the way to 10^10 for the sum of x+y+z.

Checking for x,y < 10,000 I found only one solution
(x,y,z) = (4, 5, 3)

64 + 125 = 189 = 7*27 = 7*3^3

-----------
big = 10000

for x in (range(big)):
    for y in range(x,big):
        zcubed = (x**3 + y**3)/7
        if zcubed%1 != 0:
            continue
        if not iscube(zcubed):
            continue
        z = round(zcubed**(1/3))
        if x+y+z > 10**10:
            print('too big', x,y,z)
        if gcdList([x,y,z]) != 1:
            continue
        print(x,y,z)

  Posted by Larry on 2024-04-13 13:17:07
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