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 A220129 #17 Aug 24 2025 14:35:15
%S A220129 1,1,5,3,9,1,7,1,9,3,5,1,11,1,5,3,9,1,7,1,9,3,5,1,11,1,5,3,9,1,7,1,9,
%T A220129 3,5,1,11,1,5,3,9,1,7,1,9,3,5,1,11,1,5,3,9,1,7,1,9,3,5,1,11,1,5,3,9,1,
%U A220129 7,1,9,3,5,1,11,1,5,3,9,1,7,1,9,3,5,1,11
%N A220129 1 followed by period 12: (1, 5, 3, 9, 1, 7, 1, 9, 3, 5, 1, 11) repeated; offset 0.
%C A220129 Also the number of tilings of an n X 4 rectangle using integer-sided rectangular tiles of area n.
%H A220129 Alois P. Heinz, <a href="/A220129/b220129.txt">Table of n, a(n) for n = 0..1000</a>
%F A220129 G.f.: -(10*x^6+11*x^5+16*x^4+9*x^3+7*x^2+2*x+1) / (x^6+x^5+x^4-x^2-x-1).
%e A220129 a(6) = 7, because there are 7 tilings of a 6 X 4 rectangle using integer-sided rectangular tiles of area 6:
%e A220129 ._._._._. ._._._._. ._._____. .___._._.
%e A220129 | | | | | | | | | | | | | | |
%e A220129 | | | | | |_____| | | |_____| | | | |
%e A220129 | | | | | | | | | | | |___| | |
%e A220129 | | | | | |_____| | | |_____| | | | |
%e A220129 | | | | | | | | | | | | | | |
%e A220129 |_|_|_|_| |_____|_| |_|_____| |___|_|_|
%e A220129 ._.___._. ._._.___. .___.___.
%e A220129 | | | | | | | | | | |
%e A220129 | | | | | | | | | | |
%e A220129 | |___| | | | |___| |___|___|
%e A220129 | | | | | | | | | | |
%e A220129 | | | | | | | | | | |
%e A220129 |_|___|_| |_|_|___| |___|___|
%p A220129 a:= n-> `if`(n=0, 1, [11, 1, 5, 3, 9, 1, 7, 1, 9, 3, 5, 1][irem(n, 12)+1]):
%p A220129 seq(a(n), n=0..100);
%t A220129 PadRight[{1},120,{11,1,5,3,9,1,7,1,9,3,5,1}] (* _Harvey P. Dale_, Aug 24 2025 *)
%Y A220129 Row n=4 of A220122.
%K A220129 nonn,easy,changed
%O A220129 0,3
%A A220129 _Alois P. Heinz_, Dec 06 2012