who knows why it is necessary to write:

.Sum(x => x)

Wouldn't it be enough just to write:
.Sum()

current parameter values are e.g.

nmax=83162, maxsm=1013

nmax has 5 digits

Is it going to look more like one liners in a production environment or will it be more segmented like mine?

very clever!

You don't have to hyper-optimize 5 kyu katas, my friend.

but it works, so.

nice

i really think mine should be up here

Сначала хотел через цикл for, но потом вспомнил метод floor.

Same question over here. I think it would fail if the array parameter is null, but not for empty.

Does this Linq method check for null and empty?