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

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Last modified September 20 02:19 EDT 2021. Contains 347577 sequences. (Running on oeis4.)