login
A006762
Number of strictly 2-dimensional fixed polyominoes with n cells.
(Formerly M3534)
6
0, 0, 4, 17, 61, 214, 758, 2723, 9908, 36444, 135266, 505859, 1903888, 7204872, 27394664, 104592935, 400795842, 1540820540, 5940738674, 22964779658, 88983512781, 345532572676, 1344372335522, 5239988770266, 20457802016009, 79992676367106, 313224032098242, 1228088671826971
OFFSET
1,3
COMMENTS
This sequence counts only polyominoes that are strictly 2-dimensional - it excludes those where all the squares are in a single line. Thus for n > 1, a(n) = A001168(n) - 2. - Franklin T. Adams-Watters, Jul 29 2007
REFERENCES
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
LINKS
Jean-François Alcover, Table of n, a(n) for n = 1..56
W. F. Lunnon, Counting multidimensional polyominoes, Computer Journal 18 (1975), no. 4, pp. 366-367.
FORMULA
a(n) = A001168(n) - 2 for n > 1. - Franklin T. Adams-Watters, Jul 29 2007
MATHEMATICA
A001168 = Cases[Import["https://oeis.org/A001168/b001168.txt", "Table"], {_, _}][[All, 2]];
a[n_] := If[n == 1, 0, A001168[[n]] - 2];
Array[a, 56] (* Jean-François Alcover, Sep 06 2019 *)
CROSSREFS
A column of A195739.
Cf. A001168.
Sequence in context: A202974 A034331 A107278 * A297917 A202752 A286210
KEYWORD
nonn
EXTENSIONS
Name clarified and a(18)-a(28) from Andrew Howroyd, Dec 04 2018
STATUS
approved