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 A001071 M0173 N0067 #31 Dec 23 2024 14:53:41 %S A001071 2,1,4,10,36,108,392,1363,5000,18223,67792,252938,952540,3602478, %T A001071 13699554,52296713,200406388,770411478,2970401696,11482395526, %U A001071 44491881090,172766311857,672186650116 %N A001071 Number of one-sided chessboard polyominoes with n cells. %C A001071 Two polyominoes cut from a chessboard are considered the same for this sequence if the shapes of the polyominoes are related by a rotation or translation, and the colorings are related by any symmetry including a reflection. - Joseph Myers, Oct 01 2011 %D A001071 W. F. Lunnon, personal communication. %D A001071 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). %D A001071 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A001071 Joseph Myers, <a href="https://web.archive.org/web/*/http://list.seqfan.eu/oldermail/seqfan/2010-November/013893.html">Chessboard polyominoes</a> %F A001071 a(n) = 2*O(n) - M(n) - 2*(R90(n) + R180(n)), where: %F A001071 O(n)=A000988(n), %F A001071 for even n, M(n) = A234006(n/2), otherwise 0, %F A001071 for n multiple of 4, R90(n) = A234007(n/4), otherwise 0, %F A001071 for even n, R180(n) = A234008(n/2), otherwise 0 %Y A001071 Cf. A001933, A121198. %K A001071 hard,nonn,more %O A001071 1,1 %A A001071 _N. J. A. Sloane_ %E A001071 Extended by _Joseph Myers_, Oct 01 2011 %E A001071 a(18)-a(23) by _John Mason_, Jan 02 2014