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Numbers k such that k divides 18^k - 1.
16

%I #14 Jun 06 2021 06:03:53

%S 1,17,289,4913,83521,1419857,5846759,24054337,24137569,99394903,

%T 408923729,410338673,1689713351,6951703393,6975757441,28725126967,

%U 118178957681,118285781329,118587876497,486643291847,488327158439

%N Numbers k such that k divides 18^k - 1.

%C 17 divides a(n) for n > 1.

%C a(n) = 17^(n-1) for n < 7.

%C a(7) = 20231*17^2.

%o (PARI) is(n)=Mod(18,n)^n==1 \\ _Charles R Greathouse IV_, Nov 04 2016

%Y Cf. A001026 (powers of 17), A015969 (k divides 16^k + 1).

%K hard,nonn

%O 1,2

%A _Alexander Adamchuk_, Mar 01 2007

%E a(8)-a(10) from _Farideh Firoozbakht_, Mar 05 2007

%E a(11)-a(19) from _Ryan Propper_, Dec 31 2007

%E a(20)-a(24) from _Alexander Adamchuk_, May 17 2010