A262581 - OEIS

%I #28 Nov 05 2018 17:23:59

%S 1,12,123,1234,12345,123456,1234567,12345678,123456789,12345678910,

%T 1234567891012,123456789101213,12345678910121314,1234567891012131415,

%U 123456789101213141516,12345678910121314151617,1234567891012131415161718,123456789101213141516171819,12345678910121314151617181920

%N Concatenation of the numbers from 1 to n but omitting 11.

%C There are only two primes among the first 98 terms, namely 123456789101213 and

%C 1234567891012131415161718192021222324252627282930313233343536\

%C 373839404142434445464748495051525354555657585960616263.

%C Does this sequence contain any other primes?

%C No other primes through a(10000). - _Robert Price_, Nov 05 2018

%t DeleteDuplicates[Table[FromDigits[Flatten[IntegerDigits[Complement[Range[n], {11}]]]], {n, 20}]] (* _Robert Price_, Nov 05 2018 *)

%o (PARI) terms(n) = my(s="", i=0); for(k=1, n, if(k!=11, s=concat(s, Str(k)); print1(eval(s), ", "); i++); if(i==n, break))

%o /* Print initial 20 terms as follows */

%o terms(20) \\ _Felix Fröhlich_, Nov 05 2018

%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