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 A357677 #24 Nov 11 2022 19:41:41
%S A357677 0,1,3,5,7,9,25,27,49,81,125,243,343,625,729,2187,2401,3125,6561,
%T A357677 15625,16807,19683,59049,78125,117649,177147,390625,531441,823543,
%U A357677 1594323,1953125,4782969,5764801,9765625,14348907,40353607,43046721,48828125,129140163
%N A357677 Powers of either 3 or 5 or 7 (and 0).
%C A357677 Block groups in which copies of the superblock are stored, when the "sparse superblock feature" is enabled, in the ext2/ext3/ext4 filesystems. (That is, copies of the superblock are stored in every block group when the feature is disabled, or in block groups 0, 1, 3, 5, 7, 9, 25, ... when the feature is enabled.)
%H A357677 The Linux Kernel documentation, <a href="https://www.kernel.org/doc/html/latest/filesystems/ext2.html">The Second Extended Filesystem (ext2)</a>
%H A357677 The Linux Kernel documentation, <a href="https://www.kernel.org/doc/html/latest/filesystems/ext4/globals.html">ext4 Data Structures and Algorithms</a>
%H A357677 Unix.StackExchange, <a href="https://unix.stackexchange.com/q/463473">Superblock replicas in ext4</a>
%t A357677 With[{max = 1.3*10^8}, Sort @ Flatten @ Join[{0, 1}, Table[p^Range[1, Floor[Log[p, max]]], {p, {3, 5, 7}}]]] (* _Amiram Eldar_, Oct 09 2022 *)
%Y A357677 Union of (0 and) A000244, A000351, A000420.
%K A357677 nonn,easy
%O A357677 1,3
%A A357677 _Shreevatsa R_, Oct 08 2022