This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A056797 Numbers n such that 9*10^n+1 is prime. 10
 3, 4, 5, 9, 22, 27, 36, 57, 62, 78, 201, 537, 696, 790, 905, 1038, 66886, 70500, 91836, 100613, 127240 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(22) > 2*10^5. - Robert Price, Jan 21 2015 LINKS Makoto Kamada, Prime numbers of the form 900...001. Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers. FORMULA a(n) = A100997(n) + 1. EXAMPLE For n=9 we have (9*(10^9))+1 = 9000000001, which is prime. MATHEMATICA Do[ If[ PrimeQ[9*10^n + 1], Print[n]], {n, 0, 10000}] PROG (MAGMA) [n: n in [0..1000] | IsPrime(9*10^n+1)]; // Vincenzo Librandi, May 25 2015 (PARI) is(n)=ispseudoprime(9*10^n+1) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A056806 (4*10^n+1 is prime), A100997. Sequence in context: A080552 A215176 A257041 * A029727 A086186 A014463 Adjacent sequences:  A056794 A056795 A056796 * A056798 A056799 A056800 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Aug 22 2005 EXTENSIONS a(18)-a(19) from Kamada data by Robert Price, Dec 14 2010 a(20) from Predrag Kurtovic, Sep 23 2013 a(21) from Robert Price, Jan 21 2015 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.

Last modified August 21 06:54 EDT 2019. Contains 326162 sequences. (Running on oeis4.)