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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