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 A202015 #33 Nov 26 2015 05:53:38 %S A202015 1,1,1,0,2,2,0,2,6,1,7,19,1,7,63,0,16,216,0,16,760,3,49,2725,2,48, %T A202015 9910,0,158,36446 %N A202015 Number of fixed polyominoes that can produce a repeating phenotype with 1, 2, or 4 90-degree turns. %C A202015 P is three numbers, according to 90-degree turns of a given polyomino of n squares. Each of the three numbers corresponds to a number of 90-degree turns (1, 2, and 4). Given P=(1), 3 numbers: a(1), a(2), and a(3) can be created. P=(1) refers to (1) squares in a polyomino. a(1) would be the number of 1-square polyominoes that can turn once 90 degrees and still be considered the same phenotypic shape. a(2) would be the number of 1-square polyominoes that can turn twice 90 degrees (180 degrees) and still be considered the same phenotypic shape. a(3) would be the number of 1-square polyominoes that can turn four times 90 degrees (360 degrees) and still be considered the same phenotypic shape. In other words, a(3) is the number of 1-square polyominoes that are not radially symmetric with respect to the y- and x-axes. Now, start over, and given P=(2), 3 numbers: a(4), a(5), and a(6) can be created. %H A202015 Graeme McRae, <a href="http://2000clicks.com/mathhelp/CountingPolyominoes.aspx">Polyominoes</a> %H A202015 Wikipedia, <a href="http://en.wikipedia.org/wiki/Heptomino">Heptomino Symmetry</a> %e A202015 For P=(1), a(1) = 1, a(2) = 1, and a(3) = 1. %e A202015 For P=(2), a(4) = 0, a(5) = 2, and a(6) = 2. %Y A202015 Cf. A001168 (use square animals from this list). %K A202015 nonn,more %O A202015 1,5 %A A202015 _John Michael Feuk_, Dec 08 2011