cp's OEIS Frontend

A002013 Filaments with n square cells.

%I A002013 M0835 N0317 #44 Apr 14 2025 10:26:19
%S A002013 1,1,1,2,3,7,13,31,65,154,347,824,1905,4512,10546,24935,58476,138002,
%T A002013 323894,763172,1790585,4213061,9878541,23214728,54393063,127687369,
%U A002013 298969219,701171557,1640683309,3844724417,8991137036,21054243655,49211076053
%N A002013 Filaments with n square cells.
%C A002013 Or, number of 2-sided snake polyominoes with n cells. - _Ed Pegg Jr_, May 13 2009
%D A002013 N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
%D A002013 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%D A002013 R. C. Tilley, R. G. Stanton and D. D. Cowan, The cell growth problem for filaments, pp. 310-339 in Proceedings of the Louisiana Conference on Combinatorics, Graph Theory and Computer Science. Vol. 1, edited R. C. Mullin et al., 1970.
%H A002013 Arthur O'Dwyer, <a href="https://quuxplusone.github.io/blog/2022/12/08/polyomino-snakes/">Polyomino strips, snakes, and ouroboroi</a>, Dec 10 2022.
%H A002013 Ed Pegg, Jr., <a href="http://demonstrations.wolfram.com/PolyformExplorer/">Illustrations of polyforms</a>
%H A002013 Herman Tulleken, <a href="https://www.researchgate.net/publication/333296614_Polyominoes">Polyominoes 2.2: How they fit together</a>, (2019).
%H A002013 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Polyomino.html">Polyomino</a>
%Y A002013 A333313 counts 2-sided (free) "strip" polyominoes; that is, snakes with no holes.
%Y A002013 A003104 is the polyhex analog.
%K A002013 nonn
%O A002013 0,4
%A A002013 _N. J. A. Sloane_
%E A002013 a(23) from _Joseph Myers_, Nov 22 2010
%E A002013 a(24)-a(26) from _Sean A. Irvine_, May 21 2013
%E A002013 a(27)-a(32) from _John Mason_, Dec 05 2021