A239658 Number of free triangular n-polyplets (triangular polyominoes connected at edges or corners), where turning over is allowed and holes are allowed.

1, 1, 3, 11, 75, 528, 4584, 40609, 373981, 3493723, 33079702, 316109657, 3044648053

Offset

0,3

Comments

We get triangular polyominoes when connecting over edges only (rather than edges and corners); that is A000577. The square equivalent (that is, n-polyplets) is A030222. The neighborhood is also known as the Triangular Moore neighborhood, and equals the moves of the Tri-Chess king.

Links

Table of n, a(n) for n=0..12.

Crossrefs

Cf. A000577, A030222.

Sequence in context: A374533 A203772 A290025 * A181388 A196691 A197064

Adjacent sequences: A239655 A239656 A239657 * A239659 A239660 A239661

Keyword

nonn,hard,more

Author

Abe Wits and Ragnar Groot Koerkamp, Nov 20 2020

Extensions

a(11) and a(12) from Aaron N. Siegel, May 22 2022

Status

approved