This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A128358 #14 Jun 06 2021 06:03:53 %S A128358 1,17,289,4913,83521,1419857,5846759,24054337,24137569,99394903, %T A128358 408923729,410338673,1689713351,6951703393,6975757441,28725126967, %U A128358 118178957681,118285781329,118587876497,486643291847,488327158439 %N A128358 Numbers k such that k divides 18^k - 1. %C A128358 17 divides a(n) for n > 1. %C A128358 a(n) = 17^(n-1) for n < 7. %C A128358 a(7) = 20231*17^2. %o A128358 (PARI) is(n)=Mod(18,n)^n==1 \\ _Charles R Greathouse IV_, Nov 04 2016 %Y A128358 Cf. A001026 (powers of 17), A015969 (k divides 16^k + 1). %K A128358 hard,nonn %O A128358 1,2 %A A128358 _Alexander Adamchuk_, Mar 01 2007 %E A128358 a(8)-a(10) from _Farideh Firoozbakht_, Mar 05 2007 %E A128358 a(11)-a(19) from _Ryan Propper_, Dec 31 2007 %E A128358 a(20)-a(24) from _Alexander Adamchuk_, May 17 2010