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 A348567 #12 Dec 21 2022 04:34:54 %S A348567 1,4,2,32,12,832,232,69632,14416,18719744,2876576 %N A348567 Number of fully symmetric recurrent sandpiles on an n X n grid. %F A348567 A256046(n) divides a(n), a(n) divides A348566(n, n). %e A348567 a(0) = 1, the empty sandpile on an empty grid. %e A348567 a(1) = 4, all 4 sandpiles on a 1 X 1 grid are fully symmetric. %e A348567 a(2) = 2 fully symmetric recurrent sandpiles on an 2 X 2 grid are the all-2 and all-3 sandpiles. %e A348567 Among A348566(4, 4) = 36 sandpiles with horizontal and vertical symmetry, only a(4) = 12 also have diagonal symmetries: %e A348567 3333 1331 1331 3223 3223 3333 2222 0330 2332 2332 0330 2222 %e A348567 3333 3223 3333 2222 2332 3223 2222 3223 3223 3333 3333 2332 %e A348567 3333 3223 3333 2222 2332 3223 2222 3223 3223 3333 3333 2332 %e A348567 3333 1331 1331 3223 3223 3333 2222 0330 2332 2332 0330 2222 %Y A348567 Cf. A348566, A256046. %K A348567 nonn,more %O A348567 0,2 %A A348567 _Andrey Zabolotskiy_, Oct 22 2021