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 A059683 #11 May 12 2019 09:13:07 %S A059683 1,0,3,0,2,9,0,1,12,15,0,0,12,39,25,0,0,4,59,96,35,0,0,1,42,210,188, %T A059683 49,0,0,0,21,255,550,332,63,0,0,0,4,212,954,1231,529,81,0,0,0,1,103, %U A059683 1184,2800,2406,800,99,0,0,0,0,33,964,4634,6818,4313,1142,121,0,0,0,0,6,546,5497,14182,14722,7171,1580 %N A059683 Triangle T(n,k) giving number of 3 X k polyominoes with n cells (n >= 3, 1<=k<=n-2). %C A059683 Note that for k=3 (polyominoes with square bounding rectangle) these are not the free polyominoes, because Read does not apply the full symmetry group of order 8 to reduce the fixed polyominoes for c_q(n), but only the symmetry group of order 4 (excluding the 90 deg rotations). The free polyominoes with square bounding rectangles are the z_3(n) instead. - _R. J. Mathar_, May 12 2019 %H A059683 R. C. Read, <a href="http://cms.math.ca/cjm/v14/cjm1962v14.0001-0020.pdf">Contributions to the cell growth problem</a>, Canad. J. Math., 14 (1962), 1-20. %e A059683 Triangle starts: %e A059683 1; %e A059683 0,3; %e A059683 0,2,9; %e A059683 0,1,12,15; %e A059683 ... %K A059683 nonn,easy,nice,tabl %O A059683 3,3 %A A059683 _N. J. A. Sloane_, Feb 05 2001 %E A059683 Values for n>=11 cells from _R. J. Mathar_, May 12 2019