login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A109990 Numbers n such that the string 77n is prime. 1
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 (list; graph; refs; listen; history; text; internal format)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified August 4 20:11 EDT 2021. Contains 346455 sequences. (Running on oeis4.)