Stacking balls - part I
We can stack balls like in the picture below building a tetrahedron.
A tetrahedron with three layers is chosen. Each ball is assigned an integer number which is the sum of the of the numbers on the three adjacent balls in the layer below it. We only know the numbers on the balls at the three vertices of the bottom layer and they are 1, 2 and 3 respectively. Is the number on top ball odd or even?
Inspired by Marta Reece's brick problems!
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