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A109639 Numbers n such that the string 66n is prime. 1
1, 19, 37, 53, 59, 61, 73, 79, 89, 91, 103, 107, 109, 137, 161, 169, 173, 179, 191, 221, 239, 271, 293, 301, 337, 343, 347, 359, 361, 373, 377, 383, 403, 413, 431, 449, 457, 463, 467, 491, 499, 509, 523, 529, 533, 541, 553, 569, 571, 587, 593, 601, 617, 629 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..2000

EXAMPLE

If n=1 then 66n = 661 which is a prime.

If n=91 then 66n = 6691 which is a prime.

MAPLE

a:= proc(n) local k; for k from 1 +`if`(n=1, 0, a(n-1))

      while not isprime(parse(""||66||k)) do od; a(n):=k

    end:

seq(a(n), n=1..100);  # Alois P. Heinz, Jul 30 2014

MATHEMATICA

Select[Range[700], PrimeQ[66 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *)

PROG

(MAGMA) [n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [6, 6])) ]; // Vincenzo Librandi, Jul 30 2014

CROSSREFS

Sequence in context: A139313 A272205 A245363 * A225863 A161705 A131600

Adjacent sequences:  A109636 A109637 A109638 * A109640 A109641 A109642

KEYWORD

nonn

AUTHOR

Parthasarathy Nambi, Aug 30 2005

EXTENSIONS

More terms from Vincenzo Librandi, Mar 27 2010

STATUS

approved

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Last modified March 26 05:43 EDT 2019. Contains 321481 sequences. (Running on oeis4.)