Concatenating n with n + 1

Jelly, 3 bytes

ŻVƝ

A monadic link accepting an integer which yields a list of integers

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How?

ŻVƝ - Link: integer       e.g. 59
Ż   - zero-range               [0,1,2,3,4,5,6, ... ,58,59]
  Ɲ - apply to each pair: i.e: [0,1] or [5,6]  or  [58,59]
 V  -   evaluate* jelly code   1     or 56     or  5859
    -                       -> [1,12,23,45,56, ... 5859]

* When given a list V actually joins the Python string values and evaluates that
  ...so e.g.: [58,59] -> ['58','59'] -> '5859' -> 5859

R, 32 bytes

strtoi(paste0((x=1:scan())-1,x))

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Outgolfed by MickyT, so go upvote that answer!

Python 3, 39 bytes

f=lambda n:1//n or f'{f(n-1)} {n-1}{n}'

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