A057422 Number of 2n-celled free polyominoes with 1 hole that are symmetric about two orthogonal axes (and therefore centrally symmetric) but have no other symmetries.

0, 2, 4, 12, 24, 57, 112, 244, 483, 998, 1979

Offset

4,2

Links

Table of n, a(n) for n=4..14.

Tomás Oliveira e Silva, Enumeration of polyominoes

Crossrefs

Cf. A056880.

Sequence in context: A004645 A045687 A233411 * A036045 A331392 A100538

Adjacent sequences: A057419 A057420 A057421 * A057423 A057424 A057425

Keyword

nonn,more

Author

N. J. A. Sloane, Sep 05 2000

Extensions

Name clarified by Andrei Zabolotskii, Sep 17 2025

Status

approved