A262581 Concatenation of the numbers from 1 to n but omitting 11.

1, 12, 123, 1234, 12345, 123456, 1234567, 12345678, 123456789, 12345678910, 1234567891012, 123456789101213, 12345678910121314, 1234567891012131415, 123456789101213141516, 12345678910121314151617, 1234567891012131415161718, 123456789101213141516171819, 12345678910121314151617181920

Offset: 1

Author

N. J. A. Sloane, Sep 25 2015

Keywords

• nonn
• base

Comments

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

1234567891012131415161718192021222324252627282930313233343536\

373839404142434445464748495051525354555657585960616263.

Does this sequence contain any other primes?

No other primes through a(10000). - Robert Price, Nov 05 2018

Crossrefs

Cf. A007908, A262299, A262571-A262582.

See A262300 for more about this problem.

Programs

Mathematica

DeleteDuplicates[Table[FromDigits[Flatten[IntegerDigits[Complement[Range[n], {11}]]]], {n, 20}]] (* Robert Price, Nov 05 2018 *)

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))
/* Print initial 20 terms as follows */
terms(20) \\ Felix Fröhlich, Nov 05 2018