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 A143973 #8 Feb 29 2020 03:33:20 %S A143973 2,4,1,4,1,2,5,1,1,3,4,1,1,1,1,3,1,2,4,3,2,2,1,4,1,1,2,2,3,2,1,1,2,1, %T A143973 1,1,2,3,2,4,1,2,2,2,1,1,4,1,1,3,1,2,1,2,3,2,3,2,2,1,2,1,3,1,1,4,1,3, %U A143973 1,2,1,1,3,1,1,1,1,1,1,1,3,1,1,5,1,2,1 %N A143973 Distances between multiples of 3 in A000010. %C A143973 Inspired by the question: is n == 1 mod phi(n) for n composite? %H A143973 Amiram Eldar, <a href="/A143973/b143973.txt">Table of n, a(n) for n = 1..10000</a> %F A143973 a(1) = 2 since the first two numbers k such that 3 | phi(k) are 7 and 9, and 9 - 7 = 2. %t A143973 Differences @ Position[EulerPhi[Range[200]], _?(Divisible[#, 3] &)] // Flatten (* _Amiram Eldar_, Feb 29 2020 *) %Y A143973 Cf. A000010, A008585, A066498. %K A143973 nonn %O A143973 1,1 %A A143973 J. Perry (johnandruth(AT)jrperry.orangehome.co.uk), Sep 06 2008 %E A143973 Offset corrected and more terms added by _Amiram Eldar_, Feb 29 2020