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 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 Hellström, 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

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Last modified June 16 16:46 EDT 2024. Contains 373432 sequences. (Running on oeis4.)