The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A059613 Numbers k such that 5^k - 4 is prime. 8
 5, 7, 15, 47, 81, 115, 267, 285, 7641, 19089, 25831, 32115, 59811, 70155, 178715 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(15) > 10^5. - Robert Price, Feb 03 2014 a(16) > 2*10^5. - Tyler NeSmith, Jul 25 2021 LINKS Table of n, a(n) for n=1..15. EXAMPLE 81 is present because 5^81 - 4 is prime. MATHEMATICA Select[Range[10000], PrimeQ[5^# - 4] &] (* Vincenzo Librandi, Oct 03 2012 *) PROG (PARI) is(n)=ispseudoprime(5^n-4) \\ Charles R Greathouse IV, Feb 20 2017 CROSSREFS Cf. A164785. Sequence in context: A076860 A283592 A067589 * A242503 A116048 A120282 Adjacent sequences: A059610 A059611 A059612 * A059614 A059615 A059616 KEYWORD nonn,hard,more AUTHOR Andrey V. Kulsha, Feb 07 2001 EXTENSIONS a(10)-a(14) from Robert Price, Feb 03 2014 a(15) from Tyler NeSmith, Jul 25 2021 STATUS approved

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

Last modified April 22 00:17 EDT 2024. Contains 371886 sequences. (Running on oeis4.)