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 A201253 #18 Aug 10 2025 14:09:14 %S A201253 11242770,18673200,77805000,117138840,122649450,278023200,393513120, %T A201253 881879460,2177410830,2364390210,3440848320,3919303080,5151045900, %U A201253 5836032510,7284273360,8029787220,8505803460,12998545560,13081794180,13759304790,14031484740,14104654410 %N A201253 Numbers k such that phi(k+1) = 5*phi(k). %H A201253 Giovanni Resta, <a href="/A201253/b201253.txt">Table of n, a(n) for n = 1..92</a> (terms < 10^12) %o A201253 (PARI) isok(k) = eulerphi(k+1) == 5*eulerphi(k); \\ _Michel Marcus_, Aug 10 2025 %Y A201253 Cf. A000010, A001274, A050472, A067143, A172314. %K A201253 nonn %O A201253 1,1 %A A201253 _Ray Chandler_, Nov 28 2011 %E A201253 a(9)-a(22) from _Donovan Johnson_, Nov 29 2011