Not a Problem
I type
Sequence(Sum(If(k ≠ j, Vector(Element(L_1, k), Element(L_1, j)) / Distance(Element(L_1, k), Element(L_1, j))³, 0), j, 1, 10), k, 1, 10)
What goes into the algebra list is
Sequence(Sum(If(k ≠ j, Vector(Vector(Element(L_1, k), Element(L_1, j)) / Distance(Element(L_1, k), Element(L_1, j))³), 0), j, 1, 10), k, 1, 10)
The latter is of course gibberish and so all the vectors created are of the form (?,?).
GeoGebra Classic 5.0.426.0-d (30 January 2018) running on MacOS 10.13.6
Java: 1.8.0_20
Codebase: file:/Applications/GeoGebra%205.app/Contents/Resources/Java/
OS: Mac OS X
Architecture: x86_64 / null
The same problem 
I think your command is wrong because sum must add vectors
try
Sequence(Sum(If(k ≠ j, Vector(Element(L_1, k), Element(L_1, j)) / Distance(Element(L_1, k), Element(L_1, j))³, (0,0)), j, 1, 10), k, 1, 10)
or better try
Sequence(Vector(Sum(If(k ≠ j, (Element(L_1, j) - Element(L_1, k)) / Distance(Element(L_1, k), Element(L_1, j))³, (0,0)), j, 1, 10)), k, 1, 10)
So how can I predict when and If statement must have something specific to do when the test is false and when I can just leave that empty?
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