login
A259090
Number of symmetrical n-celled polyominoes.
2
1, 1, 2, 4, 7, 15, 24, 53, 89, 194, 323, 722, 1197, 2706, 4465, 10229, 16814, 38900, 63721, 148808, 243006, 571937, 931305, 2207561, 3584959, 8551309, 13851410, 33229843, 53694326, 129485500, 208738348, 505796115, 813532119, 1980023840, 3177764415
OFFSET
1,3
LINKS
John Mason, Table of n, a(n) for n = 1..50 (This version corrects erroneous values from a(44) onwards in previous version)
T. R. Parkin, L. J. Lander, and D. R. Parkin, Polyomino Enumeration Results, presented at SIAM Fall Meeting, 1967, and accompanying letter from T. J. Lander (annotated scanned copy). See page 21. The 15th entry is not included because their value for A000105(15) was incorrect.
FORMULA
a(n) = A000105(n) - A006749(n).
MATHEMATICA
A000105 = Cases[Import["https://oeis.org/A000105/b000105.txt", "Table"], {_, _}][[All, 2]];
A006749 = Cases[Import["https://oeis.org/A006749/b006749.txt", "Table"], {_, _}][[All, 2]];
a[n_] := A000105[[n + 1]] - A006749[[n]];
Array[a, 28] (* Jean-François Alcover, Aug 27 2019 *)
CROSSREFS
Sequence in context: A333613 A171276 A027167 * A358832 A232464 A264292
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jun 18 2015
EXTENSIONS
a(5)-a(6) corrected and a(15)-a(28) from Andrew Howroyd, Dec 04 2018
a(29) and beyond from John Mason, Dec 22 2021
STATUS
approved