A110053 Numbers n such that the string 111n is the decimal expansion of a prime number.

7, 13, 17, 19, 31, 49, 59, 61, 71, 73, 77, 97, 103, 109, 119, 121, 127, 143, 149, 187, 191, 211, 217, 227, 229, 253, 263, 269, 271, 301, 317, 323, 337, 341, 347, 373, 409, 427, 431, 439, 443, 467, 487, 491, 493, 497, 509, 521, 533, 539, 577, 581, 593, 599

Offset

1,1

Links

Vincenzo Librandi, Table of n, a(n) for n = 1..2500

Example

7 is in the sequence because 1117 is prime.
73 is in the sequence because 11173 is prime.
103 is in the sequence because 111103 is prime.

Maple

a:= proc(n) local k; for k from 1 +`if`(n=1, 0, a(n-1))
      while not isprime(parse(""||111||k)) do od; a(n):=k
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, Jul 30 2014

Mathematica

Select[Range[1000], PrimeQ[FromDigits[Join[{1, 1, 1}, IntegerDigits[ # ]]]] &] (* _Alonso Delarte_, Sep 06 2005 *)
Select[Range[600], PrimeQ[111 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *)

Prog

(Magma) [ n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [1, 1, 1])) ];

Crossrefs

Sequence in context: A231607 A147603 A106084 * A276045 A230039 A226138

Adjacent sequences: A110050 A110051 A110052 * A110054 A110055 A110056

Keyword

nonn,base

Author

Parthasarathy Nambi, Sep 04 2005

Extensions

More terms from Alonso del Arte, Sep 06 2005

Status

approved