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 A128446 #15 Jul 17 2025 08:25:12
%S A128446 1,882850585445281,
%T A128446 28084773172609134470952326813135521948919663474715912134590894817085103016117634792155856629828598766188378241
%N A128446 Quotients A122000(p-1) / (2^p - 1), where p = prime(n) for n > 1.
%C A128446 A014566(n) = n^n + 1 is a Sierpinski Number of the First Kind.
%C A128446 A014566(2^n - 1) is divisible by 2^n.
%C A128446 A122000(n) = ((2^n - 1)^(2^n - 1) + 1) / 2^n = A014566(2^n - 1) / 2^n = A081216(2^n - 1).
%C A128446 a(5) = 6.044...*10^3072, and is too large to include. - _Amiram Eldar_, Jul 17 2025
%H A128446 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/SierpinskiNumberoftheFirstKind.html">Sierpinski Number of the First Kind</a>.
%F A128446 a(n) = ((2^(prime(n)-1) - 1)^(2^(prime(n)-1)-1) + 1)/(2^(prime(n)-1)*(2^prime(n)-1)).
%t A128446 a[n_] := Module[{p = Prime[n]}, ((2^(p-1) - 1)^(2^(p-1) - 1) + 1)/(2^(p-1)*(2^p-1))]; Array[a, 3, 2] (* _Amiram Eldar_, Jul 17 2025 *)
%Y A128446 Cf. A122000, A014566, A081216, A056009.
%K A128446 bref,nonn
%O A128446 2,2
%A A128446 _Alexander Adamchuk_, Mar 03 2007