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 A006758 M4114 #58 Mar 14 2021 20:46:13 %S A006758 0,0,0,1,6,17,59,195,703,2499,9188,33895,126758,476269,1802311, %T A006758 6849776,26152417,100203193,385221142,1485200847,5741256763, %U A006758 22245940544,86383382826,336093325057,1309998125639,5114451441105,19998172734785,78306011677181,307022182222505,1205243866707467,4736694001644861,18635412907198669 %N A006758 Number of strictly 2-dimensional one-sided polyominoes with n cells. %C A006758 A000988 is the main entry for this sequence. %C A006758 This version counts only polyominoes that are strictly 2-dimensional - it excludes those where all the squares are in a single line. Thus a(n) = A000988(n) - 1. - _John Mason_, Feb 18 2021 %C A006758 The value of a(11) in Table 1 (p. 366) of Lunnon (1975) is incorrect, and was corrected here by _N. J. A. Sloane_ in 2011. - _Petros Hadjicostas_, Jan 11 2019 %D A006758 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). %H A006758 N. J. A. Sloane, <a href="/A006758/b006758.txt">Table of n, a(n) for n = 0..45</a> [a(0)=0 inserted by _Georg Fischer_, Jun 25 2020] %H A006758 W. F. Lunnon, <a href="http://dx.doi.org/10.1093/comjnl/18.4.366">Counting multidimensional polyominoes</a>, Computer Journal 18 (4) (1975) 366-367. %Y A006758 A000988 (= a(n) + 1) is another version. A column of A195738. %K A006758 nonn %O A006758 0,5 %A A006758 _N. J. A. Sloane_ %E A006758 Edited by _N. J. A. Sloane_, Sep 23 2011 %E A006758 a(0)=0 inserted by _Sean A. Irvine_, Jun 24 2020 %E A006758 Name clarified by _John Mason_, Feb 18 2021