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 A387107 #13 Aug 22 2025 03:56:30 %S A387107 1,2,6,4,30,6,126,16,72,30,88,12,8190,126,150,256,131070,72,524286, %T A387107 120,1008,2728,178480,240,1800,8190,262656,1008,39672,1650,2147483646, %U A387107 65536,2397912,131070,1106280,216,616318176,524286,12743640,61680,26815350376,43344,1186422030 %N A387107 a(n) = psi(2^n-1), where psi = A002322. %F A387107 a(n) = A002322(A000225(n)). %t A387107 a[n_] := CarmichaelLambda[2^n - 1]; Array[a, 50] (* _Amiram Eldar_, Aug 16 2025 *) %o A387107 (PARI) a(n) = lcm(znstar(2^n-1)[2]); \\ _Michel Marcus_, Aug 22 2025 %Y A387107 Cf. A002322, A000225. %K A387107 nonn,changed %O A387107 1,2 %A A387107 _Emanuele Pace_, Aug 16 2025