ArcGIS Pro: Multivariate Clustering 

When you leave the Number of Clusters parameter empty, the tool will evaluate the optimal number of clusters by computing a pseudo F-statistic for clustering solutions with 2 through 30 clusters and report the optimal number of clusters in the messages window. When you specify an optional Output Table for Evaluating Number of Clusters, a chart will be created showing the pseudo F-statistic values for solutions with 2 through 30 clusters. To answer your question - there is an optional parameter in the tool named 'Output Table for Evaluating Number of Clusters' that you can use to create this table.

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