

A097970


Numbers n such that 7*10^n + 3 is prime.


2



1, 4, 6, 16, 22, 39, 103, 163, 240, 1048, 1974, 2559, 5880, 14436, 28338, 32796, 38079, 56779, 91215, 111325, 115863, 138604
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

a(23) > 2*10^5.  Robert Price, Aug 15 2015


LINKS

Table of n, a(n) for n=1..22.
Makoto Kamada, Prime numbers of the form 700...003.
Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.
Index entries for primes involving repunits.


FORMULA

a(n) = A101129(n) + 1.


EXAMPLE

For n = 1 we have 7*10^1+3 =7*10+3 = 73, which is prime.


MATHEMATICA

Do[ If[ PrimeQ[ 7*10^n + 3], Print[ n ]], {n, 0, 10000}] (* Robert G. Wilson v, Jan 19 2005 *)
Flatten[Position[Table[7 10^n+3, {n, 100000}], _?PrimeQ]] (* Harvey P. Dale, Nov 01 2011 *)
Select[Range[15000], PrimeQ[7 10^# + 3] &] (* Vincenzo Librandi, Aug 16 2015 *)


PROG

(PARI) main(m)=select(n>isprime(7*10^n + 3), vector(m, i, i)) \\ Anders HellstrÃ¶m, Aug 15 2015
(MAGMA) [n: n in [0..500]  IsPrime(7*10^n + 3)]; // Vincenzo Librandi, Aug 16 2015


CROSSREFS

Cf. A101129.
Sequence in context: A120542 A132344 A306905 * A044858 A323043 A120375
Adjacent sequences: A097967 A097968 A097969 * A097971 A097972 A097973


KEYWORD

more,nonn


AUTHOR

Julien Peter Benney (jpbenney(AT)ftml.net), Sep 07 2004


EXTENSIONS

a(10)a(13) from Robert G. Wilson v, Jan 19 2005
a(14)a(19) from Kamada data by Robert Price, Dec 14 2010
a(20)a(22) from Robert Price, Aug 15 2015


STATUS

approved



