A109990 Numbers n such that the string 77n is prime.

3, 17, 23, 27, 41, 53, 57, 59, 89, 93, 101, 137, 141, 153, 167, 171, 191, 201, 213, 237, 239, 243, 249, 261, 263, 267, 269, 279, 291, 317, 323, 339, 347, 351, 359, 369, 377, 383, 417, 419, 431, 447, 471, 477, 479, 489, 491, 509, 513, 521, 527, 543, 549, 551

Offset

1,1

Links

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

Example

If n=3 then 77n = 773 (prime).
If n=93 then 77n = 7793 (prime).

Maple

select(n -> isprime(77*10^(1+ilog10(n))+n), [$1..1000]); # Robert Israel, Jul 30 2014

Mathematica

Select[Range[700], PrimeQ[77 10^IntegerLength[#] + #] &] (* Vincenzo Librandi, Jul 30 2014 *)

Prog

(Magma) [n: n in [1..600] | IsPrime(Seqint(Intseq(n) cat [7, 7])) ]; // Vincenzo Librandi, Jul 30 2014

Crossrefs

Sequence in context: A298469 A173579 A093024 * A019369 A019380 A296937

Adjacent sequences: A109987 A109988 A109989 * A109991 A109992 A109993

Keyword

nonn,base

Author

Parthasarathy Nambi, Sep 01 2005

Extensions

More terms from Vincenzo Librandi, Mar 27 2010

Status

approved