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A109991 Numbers k such that the string 88k is prime. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified October 14 14:26 EDT 2019. Contains 328018 sequences. (Running on oeis4.)