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A390885
Number of free polyaboloes without any two triangles sharing a hypotenuse.
4
1, 2, 3, 6, 7, 13, 18, 31, 45, 76, 115, 190, 289, 472, 736, 1189, 1859, 2988, 4716, 7543, 11886, 18955, 30024, 47762, 75476, 119870, 189930, 301219, 476147, 754384, 1194531, 1890828, 2987615, 4726004, 7476387, 11818867, 18662392, 29487739, 46605846, 73603184
OFFSET
1,2
COMMENTS
Alternatively, free polyforms made of L-pipes connected end-to-end (not perpendicularly).
From Pontus von Brömssen, Nov 23 2025: (Start)
Other equivalent polyforms counted by a(n) (see linked illustration for n=6):
- free polyominoes consisting of n square cells, each of which has two adjacent chipped edges, preventing those edges from connecting to another cell;
- free polyarcs with n cells (A057787), all of which are quarter circles.
(End)
CROSSREFS
Cf. A000012 (I-pipes), A000105 (X-pipes), A000577 (Y-pipes with three 120-degree angles), A390515 (T-pipes).
Cf. A006074 (polyaboloes), A057787 (polyarcs).
Sequence in context: A330145 A183558 A328164 * A294916 A233423 A328024
KEYWORD
nonn
AUTHOR
Rhys Feltman, Nov 22 2025
EXTENSIONS
a(8)-a(32) from Pontus von Brömssen, Nov 23 2025
a(33)-a(40) from Christian Sievers, Nov 25 2025
STATUS
approved