The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A121877 Numbers k such that (5^k - 3^k)/2 = A005059(k) is prime. 53
 13, 19, 23, 31, 47, 127, 223, 281, 2083, 5281, 7411, 7433, 19051, 27239, 35863, 70327 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All terms are primes. Their indices are listed in A123704. Corresponding primes are listed in A123705. No other terms < 125000. - Robert Price, Aug 15 2011 LINKS FORMULA a(n) = prime(A123704(n)). MATHEMATICA Do[f=(5^n-3^n)/2; If[PrimeQ[f], Print[{n, f}]], {n, 1, 300}] PROG (PARI) forprime(p=2, 1e4, if(ispseudoprime((5^p-3^p)>>1), print1(p", "))) \\ Charles R Greathouse IV, Jun 16 2011 CROSSREFS Cf. A005058, A005059, A109347, A120612, A081186, A121824, A123704, A123705. Sequence in context: A007627 A180525 A257590 * A109902 A214031 A250293 Adjacent sequences:  A121874 A121875 A121876 * A121878 A121879 A121880 KEYWORD nonn,hard,more AUTHOR Alexander Adamchuk, Aug 31 2006, Oct 08 2006 EXTENSIONS More terms from Farideh Firoozbakht, Oct 11 2006 a(13)-a(16) from Robert Price, Aug 15 2011 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 January 27 02:46 EST 2020. Contains 331291 sequences. (Running on oeis4.)