This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A262571 #24 Sep 08 2022 08:46:14
%S A262571 2,23,234,2345,23456,234567,2345678,23456789,2345678910,234567891011,
%T A262571 23456789101112,2345678910111213,234567891011121314,
%U A262571 23456789101112131415,2345678910111213141516,234567891011121314151617,23456789101112131415161718,2345678910111213141516171819
%N A262571 Concatenation of the numbers from 2 to n.
%t A262571 Table[FromDigits[Flatten[IntegerDigits[Range[2, n]]]], {n, 2, 19}] (* _Robert Price_, Oct 28 2018 *)
%o A262571 (Magma) [Seqint(Reverse(&cat[Reverse(Intseq(k)): k in [2..n]])): n in [2..20]]; // _Vincenzo Librandi_, Oct 29 2018
%o A262571 (Python)
%o A262571 def a(n): return int("".join(map(str, range(2, n+1))))
%o A262571 print([a(n) for n in range(2, 20)]) # _Michael S. Branicky_, Feb 23 2021
%Y A262571 For primes in this sequence see A089987.
%Y A262571 Cf. A007908, A262299, A262572-A262582.
%Y A262571 See A262300 for more about this problem.
%K A262571 nonn,base
%O A262571 2,1
%A A262571 _N. J. A. Sloane_, Sep 25 2015