The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A348404 Number of achiral polyomino rings of length 2n with twofold rotational symmetry. 3

%I #6 Nov 14 2021 07:26:06

%S 0,1,0,1,1,3,2,6,4,14,8,30,18,71,40,155,89,358,198,786,445,1808,998,

%T 3994,2250,9158,5068

%N Number of achiral polyomino rings of length 2n with twofold rotational symmetry.

%H D. H. Redelmeier, <a href="http://dx.doi.org/10.1016/0012-365X(81)90237-5">Counting polyominoes: yet another attack</a>, Discrete Math., 36 (1981), 191-203.

%F a(n) = A348402(n) - A348403(n).

%e a(2)=1 because of:

%e OO

%e OO

%e a(4)=1 because of:

%e OOO

%e O.O

%e OOO

%e a(5)=1 because of:

%e OOOO

%e O..O

%e OOOO

%Y Cf. A348402 (all unoriented), A348403 (chiral), A324407 (unoriented with fourfold rotational symmetry), A324408 (chiral with fourfold rotational symmetry), A324409 (achiral with fourfold rotational symmetry).

%K nonn,more

%O 1,6

%A _John Mason_, Oct 18 2021

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 9 11:35 EDT 2024. Contains 375042 sequences. (Running on oeis4.)