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 A003155 M4111 #24 Jan 31 2022 03:03:42 %S A003155 1,1,1,6,15,255,1897,92263,1972653,281035054,17635484470, %T A003155 7490694495750,1405083604458437,1789509008288411290 %N A003155 Number of ways to halve an n X n chessboard. %C A003155 This is the number of ways to cut an n X n chessboard along grid lines into two identical pieces. In the case that n is odd the central square is first removed to ensure an even number of squares. Solutions that differ only by rotation or reflection are considered equivalent. - _Andrew Howroyd_, Apr 19 2016 %D A003155 M. Gardner, The Unexpected Hanging and Other Mathematical Diversions. Simon and Schuster, NY, 1969, p. 189. %D A003155 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A003155 <a href="/A003213/a003213.jpg">Illustration showing ways to quarter a 6x6 board</a> %F A003155 a(2n) = A113900(n). - _Andrew Howroyd_, Apr 19 2016 %Y A003155 Cf. A113900, A006067, A257952, A271741. %K A003155 nonn,nice %O A003155 1,4 %A A003155 _N. J. A. Sloane_ %E A003155 a(10) corrected and a(11)-a(14) from _Andrew Howroyd_, Apr 19 2016