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A097970

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

1, 4, 6, 16, 22, 39, 103, 163, 240, 1048, 1974, 2559, 5880, 14436, 28338, 32796, 38079, 56779, 91215, 111325, 115863, 138604

OFFSET

1,2

COMMENTS

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

LINKS

Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers.

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 Hellström, Aug 15 2015

(Magma) [n: n in [0..500] | IsPrime(7*10^n + 3)]; // Vincenzo Librandi, Aug 16 2015

CROSSREFS

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

URL: https://oeis.org/A097970