A109612 Numbers n such that the string 44n is prime.

3, 9, 21, 23, 41, 47, 51, 57, 63, 81, 83, 93, 101, 111, 119, 123, 129, 131, 159, 171, 179, 189, 201, 203, 207, 221, 249, 257, 263, 267, 269, 273, 279, 281, 293, 351, 357, 371, 381, 383, 389, 417, 449, 453, 483, 491, 497, 501, 507, 519, 531, 533, 537, 543, 549

Offset

1,1

Links

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

Example

If n=3 then 44n = 443 which is a prime.
If n=81 then 44n = 4481 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(""||44||k)) do od; a(n):=k
    end:
seq(a(n), n=1..100);  # Alois P. Heinz, Jul 30 2014

Mathematica

Select[Range[700], PrimeQ[44 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *)

Prog

(Magma) [n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [4, 4])) ]; // Vincenzo Librandi, Jul 30 2014

Crossrefs

Sequence in context: A291898 A330987 A365919 * A032668 A050839 A032640

Adjacent sequences: A109609 A109610 A109611 * A109613 A109614 A109615

Keyword

nonn,base

Author

Parthasarathy Nambi, Aug 30 2005

Extensions

More terms from Vincenzo Librandi, Mar 27 2010

Status

approved