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 A262575 #28 Jan 28 2024 14:46:13
%S A262575 1,12,123,1234,12346,123467,1234678,12346789,1234678910,123467891011,
%T A262575 12346789101112,1234678910111213,123467891011121314,
%U A262575 12346789101112131415,1234678910111213141516,123467891011121314151617,12346789101112131415161718,1234678910111213141516171819,123467891011121314151617181920
%N A262575 Concatenation of the numbers from 1 to n but omitting 5.
%C A262575 The only primes among the first 98 terms are 123467891011 and 123467891011121314151617. See A262552 for further primes in this sequence.
%t A262575 DeleteDuplicates[Table[FromDigits[Flatten[IntegerDigits[Complement[Range[n], {5}]]]], {n, 20}]] (* _Robert Price_, Nov 05 2018 *)
%t A262575 Join[{1,12,123,1234},Table[FromDigits[Flatten[IntegerDigits/@Drop[Range[n],{5}]]],{n,6,20}]] (* _Harvey P. Dale_, Jan 28 2024 *)
%Y A262575 Cf. A007908, A262299, A262571-A262582.
%Y A262575 See A262300 for more about this problem.
%Y A262575 For primes see A262552.
%K A262575 nonn,base
%O A262575 1,2
%A A262575 _N. J. A. Sloane_, Sep 25 2015