The seq command in Linux is used to generate a sequence of numbers from FIRST to LAST in steps of INCREMENT1. The syntax for the seq command is:
seq [OPTION]... LAST or seq [OPTION]... FIRST LAST or seq [OPTION]... FIRST INCREMENT LAST In this case, the command seq 1 5 20 has three arguments: FIRST = 1, INCREMENT = 5, and LAST = 20. This means that the command will produce numbers from 1 to 20 in steps of 5. The output will be:
1 5 10 15
The output will not include 20 because it is not a multiple of 5. The output will be printed on separate lines by default, unless a different separator is specified with the -s option2. Reference:
Seq Command in Linux [Explained With Examples]
seq Man Page - Linux - SS64.com - SS64 Command line reference