C# equivalent to range()

[Neuruss]

I'm sorry for asking about another language here, but since I only know
Python and I'm trying to write something in C#, I guess this is the
best place...

I'd like to know how to write this in C#:

x=[]
sz = 10000000
x.extend(range(sz))

My question is about "range" and "extend". Is there any equivalent in
C#?

Thanks in advance,
Neuruss