Theory for traveling salesman problem:

The following picture explains why the number of closed paths through N points in the plane is ( N - 1 ) ! / 2

Figure 1: Expalanation for: Why numberOfRoutes = (N-1)!/2

Note! If the link above does not open the image in a new tab, then copy its URL to the address bar : https://juhkarja.xyz/mot_theory_figure1.jpg
(For Figures 2,3 or 4, replace the number 1 in the URL with 2, 3 or 4).

If there are 55 points in the plane, the number of distinct closed paths is astonishingly huge.
The number of routes is far greater than the number of atoms in the Earth. 
    54! / 2      = 115421848669620690236046371341513790541639282285903970566144000000000000    (72 numbers)
    AtomsInEarth <                     1736981553974085990448491036224534347145630285403386    (52 numbers)
Figure 2: An overestimated estimate of the number of atoms in the Earth


There are many calculators on the internet that can compute with high precision. For example
https://www.mathsisfun.com/calculator-precision.html
Another one is WolframAlpha, which also accepts to add calculations to a URL
Direct calculation of 54! / 2 on WolframAlpha : https://www.wolframalpha.com/input?i=54!%2F2

Figure 3: Even though there is an unbelievable number of routes, the shortest is still findable in the 55-point case.

Figure 4: This image shows why the convex hull is a good starting point for finding the shortest path..