

A265487


Numbers k such that 81^k  9^k  1 is prime.


1



1, 3, 10, 18, 70, 585, 921, 1943, 4635, 13543, 13803, 15938, 39004
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OFFSET

1,2


COMMENTS

2*a(n) is in A265481.
For k = 1, 3, 10, 18 the corresponding primes are 71, 530711, 12157665455570144399, 22528399544939174261745512577773519.
a(n) is not of the form 5*k+2 (divisibility by 11), 9*k+2 (divisibility by 19), 7*k+2*(1)^k+7 (divisibility by 29), 15*k+2 (divisibility by 31) or 29*k+8 (divisibility by 59).
a(14) > 10^5.  Robert Price, Apr 21 2020


LINKS

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


EXAMPLE

3 is in the sequence because 81^3  9^3  1 = 530711 is prime.


MATHEMATICA

Select[Range[1000], PrimeQ[81^#  9^#  1] &]


PROG

(MAGMA) [n: n in [0..500]  IsPrime(81^n9^n1)];
(PARI) for(n=1, 1e3, if(ispseudoprime(81^n  9^n  1), print1(n, ", "))) \\ Altug Alkan, Dec 12 2015


CROSSREFS

Cf. similar sequences listed in A265481.
Sequence in context: A275988 A177955 A298976 * A074893 A074178 A178996
Adjacent sequences: A265484 A265485 A265486 * A265488 A265489 A265490


KEYWORD

nonn,more


AUTHOR

Vincenzo Librandi, Dec 12 2015


EXTENSIONS

a(9) from Altug Alkan, Dec 12 2015
a(10)a(13) computed from A265481 by Ray Chandler, Sep 25 2019


STATUS

approved



