ls all files in sequence. How to?

Shell Programming and Scripting
1

Hi, all:

Newbie questions:

For example, if I have 6 files, respectively named as:

How to "ls" all files in sequence of two ways?

1) The first way is according to the sequence of the natural number.
Say, the same sequence as shown as they are given.

2) The second way is default Linux way. My "ls" directly gives:

jiapei@jiapei-laptop:~/Desktop/test$ ls
10.txt  11.txt  1.txt  20.txt  2.txt  3.txt

Some times, we may need the 2nd way to display all files, but most of the times, we will go for the 1st way to display all files. My question is just "how to"?

Cheers
JIA

2 
$ ls | sort -nt. -k1,1    
1.txt
2.txt
3.txt
10.txt
11.txt
20.txt
3

Thank you, but what does

k1,1

mean?
and why

-nt.

??

I tried

ls | sort -n

it works already.