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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
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
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, May 07 2004
STATUS
approved