A109991 Numbers k such that the string 88k is prime.

1, 3, 7, 19, 21, 31, 37, 39, 49, 61, 63, 67, 87, 93, 117, 129, 169, 177, 211, 223, 237, 241, 259, 261, 289, 301, 321, 327, 337, 339, 379, 397, 411, 423, 427, 463, 469, 471, 493, 499, 513, 523, 547, 589, 591, 607, 609, 643, 651, 657, 661, 663, 667, 681, 721, 729

Offset

1,2

Links

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

Example

If k=1 then 88k = 881, which is prime.
If k=61 then 88k = 8861, which is prime.

Maple

a:= proc(n) local k; for k from 1 +`if`(n=1, 0, a(n-1))
      while not isprime(parse(""||88||k)) do od; a(n):=k
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, Jul 30 2014

Mathematica

Select[Range[900], PrimeQ[88 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *)

Prog

(Magma) [n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [8, 8])) ]; // Vincenzo Librandi, Jul 30 2014

Crossrefs

Sequence in context: A032675 A089749 A032667 * A248219 A322963 A018432

Adjacent sequences: A109988 A109989 A109990 * A109992 A109993 A109994

Keyword

nonn,base

Author

Parthasarathy Nambi, Sep 01 2005

Extensions

More terms from Vincenzo Librandi, Mar 27 2010

Status

approved