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

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A072164 Numbers k >= 1 such that f(k) = k^k - (k-1)^(k-1) is prime. 7
 2, 3, 4, 7, 11, 17, 106, 120, 1907, 7918 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Enoch Haga proposed studying the primality of f(k) and he already knew the first 4 solutions. C. Rivera found the next four solutions using Ubasic and the last one using PRIMEFORM. Currently f(1907) is only a probable prime number, according to PRIMEFORM. No other k < 25000. - T. D. Noe, Jun 12 2008 LINKS Table of n, a(n) for n=1..10. C. Rivera, Puzzle 185 Eric Weisstein's World of Mathematics, Power Difference Prime Eric Weisstein's World of Mathematics, Integer Sequence Primes EXAMPLE 2^2 - 1^1 = 3 is prime. MATHEMATICA Select[Range[2, 200], PrimeQ[ #^#-(#-1)^(#-1)]&] (* T. D. Noe, Jun 12 2008 *) PROG (PARI) isok(k) = ispseudoprime(k^k - (k-1)^(k-1)); \\ Jinyuan Wang, Mar 19 2020 CROSSREFS Cf. A007781 (n^n-(n-1)^(n-1)). Equals A140669 + 1. Sequence in context: A346020 A192669 A339484 * A060987 A359743 A006259 Adjacent sequences: A072161 A072162 A072163 * A072165 A072166 A072167 KEYWORD nonn,hard,more AUTHOR Carlos Rivera, Jun 28 2002 EXTENSIONS 7918 found by Henri Lifchitz in 2001, contributed by Eric W. Weisstein, Nov 29 2005 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 July 22 18:23 EDT 2024. Contains 374540 sequences. (Running on oeis4.)