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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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

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.

FORMULA

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

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 *)

CROSSREFS

A row of A094166.

Cf. A001420.

Sequence in context: A049220 A094790 A007822 * A094803 A094826 A033190

Adjacent sequences: A094161 A094162 A094163 * A094165 A094166 A094167

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, May 07 2004

STATUS

approved