Expression: k[s[k]][k[k[s]][s[s]]][s[s][k[s][s][k[k][s]][s[s[k][k]]][k[k]][s[s][k[s[k]]][s[k][k[s[s][k[k]]][k[s]]]][k[k[s][s[s[k][k]]]]]]]]

Visualisation: Initial state and first 5 steps of evaluation:  The nth row of the image represents the nth step of evaluation of the combinator.   

Graph of Evaluated Expression Lengths: As the combinator is evaluated, its length changes. This graph plots length of combinator against number of steps of evaluation.  

Statistical Analysis of Halting Time: This combinator has 43 leaves.
This combinator falls within the 19th percentile of a random sample of 1000 combinators with leaf size 43, halting after 5 steps  on average, 19.9% of combinators from this sample halt before this one.
A graph demonstrating this follows:  

Machine Learning Analysis of Halting: A machine learning model (using logistic regression) has been trained on a sample of 1456 rasterised images of the first 5 steps of random SK combinator expressions with varying leaf lengths, achieving 87.7% accuracy when classifying a test set of 1454 random SK combinator expressions as halting or non halting (before 40 steps).  This particular expression, which halts after 5 step(s), is classified as having a Indeterminate% probability of halting, and a Indeterminate% probability of not halting (before 40 steps). 

Evaluated expression: Halted in 4 step(s)  0  k[s[k]][k[k[s]][s[s]]][s[s][k[s][s][k[k][s]][s[s[k][k]]][k[k]][s[s][k[s[k]]][s[k][k[s[s][k[k]]][k[s]]]][k[k[s][s[s[k][k]]]]]]]]  1  s[k][s[s][s[k][s[s[k][k]]][k[k]][s[s[k][k[s[s][k[k]]][k[s]]]][k[s[k]][s[k][k[s[s][k[k]]][k[s]]]]][k[s]]]]]  2  s[k][s[s][k[k[k]][s[s[k][k]][k[k]]][s[k][k[s[s][k[k]]][k[s]]][k[s]][k[s[k]][s[k][k[s[s][k[k]]][k[s]]]][k[s]]]]]]  3  s[k][s[s][k[k][k[k[s]][k[s[s][k[k]]][k[s]][k[s]]][s[k][k[s]]]]]]  4  s[k][s[s][k]] 

