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 A262576 #27 Nov 05 2018 17:25:23
%S A262576 1,12,123,1234,12345,123457,1234578,12345789,1234578910,123457891011,
%T A262576 12345789101112,1234578910111213,123457891011121314,
%U A262576 12345789101112131415,1234578910111213141516,123457891011121314151617,12345789101112131415161718,1234578910111213141516171819,123457891011121314151617181920
%N A262576 Concatenation of the numbers from 1 to n but omitting 6.
%C A262576 The only prime among the first 98 terms is a(6) = 123457. Does the sequence contain any other primes?
%C A262576 No additional primes through the first 2000 terms. - _Harvey P. Dale_, Sep 27 2018
%C A262576 Differs from A132943 at about the 28th terms.
%C A262576 No primes, other than a(6), through a(10000). - _Robert Price_, Nov 03 2018
%t A262576 Module[{nn=20,c},c=Drop[Range[nn],{6}];Table[FromDigits[Flatten[ IntegerDigits/@ Take[c,n]]],{n,nn-1}]] (* _Harvey P. Dale_, Sep 27 2018 *)
%Y A262576 Cf. A132943.
%Y A262576 Cf. A007908, A262299, A262571-A262582.
%Y A262576 See A262300 for more about this problem.
%K A262576 nonn,base
%O A262576 1,2
%A A262576 _N. J. A. Sloane_, Sep 25 2015