%I #28 Sep 17 2019 17:25:13
%S 1,12,124,1245,12456,124567,1245678,12456789,1245678910,124567891011,
%T 12456789101112,1245678910111213,124567891011121314,
%U 12456789101112131415,1245678910111213141516,124567891011121314151617,12456789101112131415161718,1245678910111213141516171819,124567891011121314151617181920
%N Concatenation of the numbers from 1 to n but omitting 3.
%C The only prime among the first 98 terms is a(6) = 124567. Does the sequence contain any other primes?
%C No other primes through a(10000). - _Robert Price_, Nov 04 2018
%t DeleteDuplicates[Table[FromDigits[Flatten[IntegerDigits[Complement[Range[n], {3}]]]], {n, 20}]] (* _Robert Price_, Nov 05 2018 *)
%t Join[{1,12},Table[FromDigits[Join[{1,2},Flatten[IntegerDigits/@Range[4,n]]]],{n,4,20}]] (* _Harvey P. Dale_, Sep 17 2019 *)
%Y Cf. A007908, A262299, A262571-A262582.
%Y See A262300 for more about this problem.
%K nonn,base
%O 1,2
%A _N. J. A. Sloane_, Sep 25 2015
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