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 A127101 #16 May 21 2024 01:12:43 %S A127101 1,2,4,8,10,20,40,110,136,164,220,328,440,610,680,820,1210,1220,1544, %T A127101 1640,2420,2440,2530,4840,5060,5576,6710,7370,7480,7720,9020,10120, %U A127101 11810,13420,13612,14008,14740,18040,18632,19580 %N A127101 Numbers k such that k^2 divides 9^k - 1. %H A127101 Amiram Eldar, <a href="/A127101/b127101.txt">Table of n, a(n) for n = 1..3000</a> (terms 1..56 from R. J. Mathar) %t A127101 Select[Range[20000], IntegerQ[(PowerMod[9, #, #^2 ]-1)/#^2 ]&] %o A127101 (PARI) is(k) = Mod(9, k^2)^k == 1; \\ _Amiram Eldar_, May 21 2024 %Y A127101 Subset of A068382 (numbers k such that k divides 9^k - 1). %Y A127101 Cf. A127100, A127102, A127103, A123104, A127105, A127106, A127107, A127092. %K A127101 nonn %O A127101 1,2 %A A127101 _Alexander Adamchuk_, Jan 05 2007