C# (Visual C# Compiler), 46 bytes

If you are allowed to have some using static directives in the top whose bytes do not count:

n=>1+Concat(Range(1,n-1).Select(x=>","+x+++x)) 

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Will explode if input n is 0.

It is interesting that, while the C# rules say ","+x+++x means ( "," + (x++) ) + x, if it had meant ( "," + x ) + (++x) instead, the program would still work!

Clojure, 54 bytes

#(reduce(fn[a n](conj a(str n(inc n))))[1](range 1 %)) 

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Just a reduction over a range between 1 (inclusive) and n (exclusive).

(defn concat-n-n+1 [n] (reduce (fn [acc m] (conj acc (str m (inc m)))) [1] (range 1 n))) 

The first element of the list is a number, the rest are strings. This seems to be allowed by the spec.

K (oK), 12 bytes

Solution:

,/'$1,2':1+! 

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Examples:

,/'$1,2':1+!1 ,,"1" ,/'$1,2':1+!2 (,"1" "12") ,/'$1,2':1+!3 (,"1" "12" "23") ,/'$1,2':1+!10 (,"1" "12" "23" "34" "45" "56" "67" "78" "89" "910") 

Explanation:

,/'$1,2':1+! / the solution ! / range 0..n 1+ / add 1 2': / sliding window of 2 1, / prepend 1 $ / convert to strings ,/' / flatten each 

C Sharp 51 bytes

n=>new int[n].Select((_,o)=>int.Parse($"{o}{o+1}")) 

Attache, 15 bytes

{N!_'-~_}=>Iota 

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Explanation

{N!_'-~_}=>Iota { }=> map the inside function: Iota (over each number k from 0 to n-1) ' array concatenate: _ k -~_ k+1 N! convert [k, k + 1] to an integer (concatenates and returns a number) 

Rutger, 108 bytes

x=$Input; f=For[$x]; f=f[@i]; f=f[{p=Subtract[$i];r=Concat[Str[p[1]]];Print[Integer[r[Str[$i]]]];}]; Do[$f]; 

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Ungolfed

input = $Input; for = For[$input]; for = for[@index]; for = for[{ dec = Subtract[$index]; ret = Concat[Str[dec[1]]]; Print[Integer[ret[Str[$index]]]]; }]; Do[$for]; 

The basic concept of Rutger is the lack of multi-adic commands: every command takes a single argument, and if the command needs multiple argument, each new call returns a curried function.

First, we take evaluated input and store it in \$x\$. We then create a For object, a tri-adic command. The first two calls create a variable \$f\$, that will loop \$x\$ times, using the iteration variable \$i\$, starting at \$i := 1\$. The third call indicates the code to be run:

{p=Subtract[$i];r=Concat[Str[p[1]]];Print[Integer[r[Str[$i]]]];} 

This creates a block of code containing 3 statements. Our first two are variable assignments. First, we create a curried function Subtract[$i], which prepares to subtract a value from \$i\$. This curried function is saved in the \$p\$ variable. Next, we create a second curried variable, \$r\$, which starts by calling p[1], subtracting \$1\$ from \$i\$. We then convert \$i-1\$ to a string and pass it as the first argument to the Concat function. Finally, we convert \$i\$ to a string, concatenate it to \$str(i - 1)\$ and convert it to an integer to reomve the leading \$0\$ when \$i = 1\$. This is then printed.

The last line, Do[$f];, runs the for loop.

RAD, 72 bytes

0,(⊢+10×⊣)⍁¨∊¨(⌽∘⌊(⊢|⍨10*(⍳(1+∘⌊10⍟⊢)))÷10*1-⍨(⍳(1+∘⌊10⍟⊢)))¨¨(⊢,1+⊢)¨⍳⎕ 

Link to repository

I wanted to try to see if I could do it in a "non-mathematical" way by splitting a number up into its digits.

C, 39 bytes

x(n){n&&x(n-1);printf("%d%d, ",n,n+1);} 

eliminated the ternary conditional and shaved off 3 bytes.

ARBLE, 23 20 bytes

Saved a handful of bytes by using better named variables.

range(0,n)//(x..y|0) 

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Python 2.7, 52 bytes

I tried my best. Not yet familiar with this golfing thing.

def a(n): for e in range(n): print int(`e`+`e+1`) 

The int() removes the leading zero in the first output, as specified in the rules.

Twig, 72 bytes

Twig is very verbose, causing some issues when trying to reduce the length.

{%macro f(a)%}{%for i in 1..a%}{{o~i}} {%set o=i%}{%endfor%}{%endmacro%} 

This requires that "strict variables" is disabled (default).

How to use?

Simply import the macro and call it:

{% import "fn.twig" as fn %} {{ fn.f(<number>) }} 

You can test it on https://twigfiddle.com/lah1a5

Haskell, 35 bytes

f n="1":map(show.(-1+)<>show)[2..n] 

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Explanation / Ungolfed

The operator (<>) is the addition of Semigroups, in case of the Semigroup a -> b (where b needs to be a Semigroup) it is defined as:

(f <> g) = \x-> f x <> g x 

And in case of the Semigroup String it is the same as concatenation, so the code becomes:

f n = "1" : map (\x-> show (x-1) ++ show x) [2..n] 

_{1 (imports (<>) since it's not part of the Prelude in GHC 8.2.2)}

TI-Basic, 22 bytes

:seq(A,A,1,Ans :Ans+(Ans-1)10^(1+int(log(Ans 

Bash, 56 bytes

echo 1;for i in $(seq $(($1-1)));do echo $i$((i+1));done 

A pretty naive approach.

Lua, 62 bytes

loadstring't={1}for i=2,(...)do t[#t+1]=(i-1)..i end return t' 

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Explanation

This is an anonymous function.

t={1} -- initializes the return table, with the number 1 already in it for i = 2, (...) do -- loop from 2 to the number of the input -- (this is actual code, ... gets the arguments of the program/function t[#t+1] = (i-1)..i -- append to the table i-1 concatenated with i end return t -- returns the table 

Swift 4, 43 bytes

print(1);(1..<n).map{print("\($0)\($0+1)")} 

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n is the input of the program

Noether, 15 bytes

I(iWi1+W+WP?!i) 

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Explanation

I( ) - Loop until the top of the stack equals the input iW - Push i and convert it to a string i1+W - Add one to i and convert to string + - Concatenate two strings WP - Convert string to a number and print it ? - Print a newline !i - Increment i 

VBA (Excel), 31 bytes

using immediate window and Cell [A1] as input

for x=1to[a1]:?int(x-1 &x):next

Python 2, 42 bytes

I know there are plenty of shorter answers already.

a=0 exec"print`a`[:a]+`a+1`;a+=1;"*input() 

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Pepe, 68 bytes

RrEEEEEREeErREEREEEEEREErEEEEEeEErEEEereEEreeErEEEEEeeEReerREEREeRee 

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Previous code has errors when giving input 0, so this is fixed!

Explanation:

# Preparation RrEEEEE # Stack r: [0, 1] REeE # Stack R: [input] # Loop rREE # create label input (r flag: skip until REe) REEEEE # increment input (loop preparation) REE # create label input rEEEEEeEE # join all rEEEe # move r pointer to last reEE # output as int reeE # output newline "\n" rEEEEEeeE # increment all Ree # repeat if input != last content of stack rREE # create label input + 1 (r flag: skip until REe) REe # stop skipping commands Ree # if not 0, go to loop 

Microscript II, 16 bytes

1vsN-s{lPps1+v}* 

Output is newline-separated.

Gol><>, 11 bytes

IFLL?nLPN|; 

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Explanation:

IFLL?nLPN|; I //Take a number as input F //Loop as many times as the input specified LL // Push the loop counter twice to the stack (same as L:) ?n // Check wether the count is zero, if not print the counter as the first digit LP // Push the loop counter and add 1 N // Output the next digits of the number with nl |; //Exit code 

Dart, 46 45 bytes

f(n)=>List.generate(n,(e)=>e<1?1:'$e${e+1}'); 

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Kotlin, 43 41 bytes

{(1..it).mapIndexed{i,v->"$i$v".toInt()}} 

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Knight, 29 bytes

;=n+0P;=i 0W>n iO+0++""i=i+1i 

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Gema, 42 characters

*=@repeat{*;${n;}@set{n;@add{${n;};1}}$n } 

Sample run:

bash-5.1$ gema '*=@repeat{*;${n;}@set{n;@add{${n;};1}}$n }' <<< 5 1 12 23 34 45 

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Ly, 12 bytes

Rrp[:u`u' o] 

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This is pretty brute force, but short enough to warrant a post I think...

R - generate an inclusive rangefrom "0" to the STDIN number rp - reverse the stack, delete the "0" [ ] - for each number on the stack... :u - duplicate number, print it `u - increment the number, print it ' o - print a space 

AWK, 26 bytes

a=$1{for(;a;a--)$a=a a+1}1 

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Turns out that a version in AWK is pretty short too, so here's that one...

a=$1 - stash the number we want { } - code always runs if STDIN>0 for(;a;a--) - loop for N, N-1, N-2, ... 1 $a=a a+1 - set positional var to N appended w/ N+1 1 - print all the positional vars we just set 

This really just abuses the fact that AWK will reset the positional variable count if you set them to a value. And it uses a "truthy" condition with no associated code block to print them all.

SAS

Input is passed by:

%let n=123; 

4GL - 38

data; do i=1to &n;x=cats(i-1,i)+0;put x;end; run; 

The data; and run; are obligatory for every 4GL data step, so the code effectively doing the job is in line 2.

Macrolanguage - 44

%macro m(n,x);%do i=1%to&n;%put&x&i;%let x=&i;%end; %mend; 

The %macro and %mend; are obligatory for every Macroprogram, so the code effectively doing the job is in line 2.

To run macro execute:

%m(&n) 

Vyxal, 29 bits^v2, 3.625 bytes

ʀzṅ⌊ 

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Explained

ɾzṅ ɾ # range [1, input] z # overlapping pairs (equivalent to 2l) ṅ # concatenate each pair into a single string 

SAKO, 85 bytes

PODPROGRAM:F(N) *)DRUKUJ(9,0):(I-1)×10*ENT(((LN(I))/LN(10))+1)+I POWTORZ:I=1(1)N WROC 

I use here a quite simple approach:
We take a number I, multiply it by 10*(length of I+1), add I+1 to it, and print the result. It's repeated until I+1 = N.

I just use here I-1 and I instead for some byte saving.

Full programme version, 87 bytes

CZYTAJ:N *1)DRUKUJ(9,0):(I-1)×10*ENT(((LN(I))/LN(10))+1)+I POWTORZ:I=1(1)N STOP1 KONIEC