I expect the last index to be 19.

Why? The range is 0 .. 20 inclusive: 

[ 6:17:58.02] C:\test>ranges -M=20 -N=3
 0 : from       0 to       6 (      7)
 1 : from       7 to      13 (      7)
 2 : from      14 to      20 (      7)
========================================
                                   21

[ 7:10:34.53] C:\test>ranges -M=20 -N=2
 0 : from       0 to       9 (     10)
 1 : from      10 to      20 (     11)
========================================
                                   21

[ 7:11:36.69] C:\test>ranges -M=20 -N=1
 0 : from       0 to      20 (     21)
========================================
                                   21

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In reply to Re^5: Split range 0 to M into N non-overlapping (roughly equal) ranges. by BrowserUk
in thread Split range 0 to M into N non-overlapping (roughly equal) ranges. by BrowserUk

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