A002013 Filaments with n square cells.

1, 1, 1, 2, 3, 7, 13, 31, 65, 154, 347, 824, 1905, 4512, 10546, 24935, 58476, 138002, 323894, 763172, 1790585, 4213061, 9878541, 23214728, 54393063, 127687369, 298969219, 701171557, 1640683309, 3844724417, 8991137036, 21054243655, 49211076053

Offset: 0

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Or, number of 2-sided snake polyominoes with n cells. - Ed Pegg Jr, May 13 2009

References

• N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
• 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.

Links

• Arthur O'Dwyer, Polyomino strips, snakes, and ouroboroi, Dec 10 2022.
• Ed Pegg, Jr., Illustrations of polyforms
• Herman Tulleken, Polyominoes 2.2: How they fit together, (2019).
• Eric Weisstein's World of Mathematics, Polyomino

Crossrefs

A333313 counts 2-sided (free) "strip" polyominoes; that is, snakes with no holes.

A003104 is the polyhex analog.

Extensions

a(23) from Joseph Myers, Nov 22 2010

a(24)-a(26) from Sean A. Irvine, May 21 2013

a(27)-a(32) from John Mason, Dec 05 2021