A109387 Numbers k such that 3^k - k^3 is prime.

1, 4, 10, 52, 112, 212, 346, 406, 512, 13904, 76610, 89746, 114892

Offset

1,2

Comments

Terms <= 512 correspond to certified primes. Next term after 13904 is greater than 20000.

Links

Table of n, a(n) for n=1..13.

Example

4 is a term because 3^4 - 4^3 = 17 is prime.
3^10 - 10^3 = 58049 is prime, hence 10 is a term.

Mathematica

Do[If[PrimeQ[3^n - n^3], Print[n]], {n, 1, 20000}]

Prog

(PARI) is(n)=isprime(3^n-n^3) \\ Charles R Greathouse IV, Feb 17 2017

Crossrefs

Sequence in context: A351046 A208236 A032495 * A362819 A018844 A007027

Adjacent sequences: A109384 A109385 A109386 * A109388 A109389 A109390

Keyword

hard,more,nonn

Author

Ryan Propper, Jun 26 2005

Extensions

Two more terms from Donovan Johnson, Feb 26 2008

a(13) from Norbert Schneider submitted by Robert Price, Mar 16 2019

Status

approved