A094164 Number of rooted 2-dimensional polyominoes with n triangular cells, with no symmetries removed.

1, 3, 9, 28, 90, 282, 875, 2700, 8271, 25265, 77088, 235014, 716261, 2182257, 6646200, 20234080, 61581327, 187366482, 569947883, 1733389620, 5270937735, 16025807017, 48719131461, 148092422604, 450116618125, 1367983011213, 4157227183617

Offset: 1

Author

N. J. A. Sloane, May 07 2004

Keywords

• nonn

References

• Dan Hoey, Bill Gosper and Richard C. Schroeppel, Discussions in Math-Fun Mailing list, circa Jul 13 1999.

Links

• Jean-François Alcover, Table of n, a(n) for n = 1..32
• R. C. Schroeppel, A few mathematical experiments, Experimental Mathematics Workshop, Oakland, 2004.

Crossrefs

A row of A094166.

Cf. A001420.

Programs

Mathematica

A001420 = Cases[Import["https://oeis.org/A001420/b001420.txt", "Table"], {, }][[All, 2]];
a[n_] := n * A001420[[n]] / 2;
Array[a, 27] (* Jean-François Alcover, Sep 08 2019 *)

Formula

a(n) = n * A001420(n) / 2. - Andrew Howroyd, Dec 04 2018