Question: how many routes in a 4x4 square

The verticies are of a 4x4 square, 16 in total.  You may cross a verticie only once, and you can move horizontally, vertically and diagonally.

Lets label the verticals  a,b,c,d and from bottom to top 1,2,3,4.  How would you find all the routes with a travel length of 6?

 

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