A390515 Number of free polyforms made of T-pipes connected end-to-end (not perpendicular).

1, 4, 15, 99, 630, 4599, 34099, 261603, 2036026, 16075980, 128214840, 1031495768

Offset

1,2

Comments

Equivalently, a(n) is the number of free polyominoes consisting of n square cells, each of which has one chipped edge, preventing that edge from connecting to another cell. See linked illustrations. - Pontus von Brömssen, Nov 12 2025

Links

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

Pontus von Brömssen, The 4 polyominoes with 2 cells, each of which has one chipped edge.

Pontus von Brömssen, The 15 polyominoes with 3 cells, each of which has one chipped edge.

Pontus von Brömssen, The 99 polyominoes with 4 cells, each of which has one chipped edge.

Pontus von Brömssen, Alternative illustration for 4 cells.

Rhys Feltman, Polytees - Polypad.

Rhys Feltman, Polytees - Rhys' Polyform Atlas.

Index entries for sequences related to polyominoes.

Crossrefs

Cf. A000012 (I-pipes), A000105 (X-pipes), A000577 (Y-pipes with three 120-degree angles).

Sequence in context: A352415 A079128 A377326 * A368191 A356524 A289489

Adjacent sequences: A390512 A390513 A390514 * A390516 A390517 A390518

Keyword

nonn,more

Author

Rhys Feltman, Nov 08 2025

Extensions

a(4)-a(9) from Pontus von Brömssen, Nov 13 2025

a(10)-a(12) from Christian Sievers, Nov 19 2025

Status

approved