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 A281909 #19 Mar 06 2017 12:27:29 %S A281909 2,3,7,7,25,25,49,49,49,49,49,49,81,81,81,81,241,241,289,289,289,289, %T A281909 289,289,289,289,289,289,289,289,721,721,721,721,721,721,961,961,961, %U A281909 961,961,961 %N A281909 Smallest k such that k^i - 1 is a totient number (A002202) for all i = 1 to n, or 0 if no such k exists. %e A281909 a(3) = 7 because 7 - 1 = 6, 7^2 - 1 = 48, 7^3 - 1 = 342 are all totient numbers and 7 is the least number with this property. %Y A281909 Cf. A000010, A002202, A045542. %K A281909 nonn,more %O A281909 1,1 %A A281909 _Altug Alkan_, Feb 01 2017 %E A281909 a(18)-a(42) from _Max Alekseyev_, Feb 07 2017, Mar 06 2017