Thanks for explaining.
Did you try installing [the `seq` utility](https://en.wikipedia.org/wiki/Seq_(Unix))? It's part of GNU Coreutils, and seems to also [be available on BSDs](https://man.openbsd.org/FreeBSD-11.1/seq.1).
Hmm.. that seems to be showing results for FreeBSD man pages on openbsd.org. Note the results here: https://man.openbsd.org/OpenBSD-6.4/seq.1 (which are none).
I installed the coreutils package, but `seq` still isn't available.
Here's a related thread on an unrelated project [seq(1) is not available on OpenBSD](https://github.com/pyenv/pyenv/pull/1166)