Power Query List insert range at irregular intervals

Hello, Richard. c stands for a record field name I defined in this function call. List.Generate in this implementation generates a list of records with fields i, c and s. i field works as counter to access particular item of original list recs. To illustrate what's going on - simply remove 4th optional argument of List.Generate and see what you get as gen. You'll see a list of records with fields and values - this is how List.Generate works. Don't be fooled with x variable. It has different meaning in 2, 3 and 4th argument. Read documentation. In 3rd argument (which generates next item list in our sequence) it refers to previously generated item. So that when we write (x) => [i = x[i] + 1, ...] we simply create next item (next record in our list) with counter field = prev counter + 1.
So that List.Generate has an access to the very last item it created. It's useful for rolling totals etc.
At the same time don't forget that we can calculate record field values using fields of the same record. So that [c = 25, s = c + 5] is valid syntax and yields [c = 25, s = 30].
I can't teach you everything here. Watch some vids, read documentation, solve problems etc.

Thank you for taking the time to respond, I'm going to have to get rick de groot and whatshername's book. I find him pretty good, his list generate Fibonacci sequence gave me the basics for records,
have not had a chance to work through yet, but will,

Thanks again,

RD