A319324 a(n) is the number of fixed polyglasses (polyiamonds which need only touch at corners) with n cells.

2, 12, 88, 710, 6054, 53500, 484784, 4475010, 41902626, 396838992, 3793117200, 36534684066

Offset

1,1

Comments

Polyglasses are to polyiamonds (A001420) as polyplets (A006770) are to polyominoes (A001168). The name derives from the 2-celled animal (diglass) which looks like an hourglass.

Links

Table of n, a(n) for n=1..12.

David Bevan, The 88 fixed triglasses.

Adam Gruber, Java program to count lattice animals.

Example

a(2) = 12: three rotations of a diamond, three rotations of an hourglass and six rotations of "two mountains".

Crossrefs

Cf. A001420 (fixed polyiamonds), A319325 (row convex polyglasses), A319326 (column convex polyglasses).

Sequence in context: A193125 A305868 A356830 * A059435 A192621 A372090

Adjacent sequences: A319321 A319322 A319323 * A319325 A319326 A319327

Keyword

nonn,more,hard

Author

David Bevan, Sep 18 2018

Extensions

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

Status

approved