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Number of fixed polyominoes with 2n cells.
7

%I #12 Sep 22 2019 11:49:23

%S 2,19,216,2725,36446,505861,7204874,104592937,1540820542,22964779660,

%T 345532572678,5239988770268,79992676367108,1228088671826973,

%U 18946775782611174,293560133910477776,4565553929115769162,71242712815411950635

%N Number of fixed polyominoes with 2n cells.

%H Jean-François Alcover, <a href="/A210986/b210986.txt">Table of n, a(n) for n = 1..28</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/Polyomino.html">Polyomino</a>

%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Polyomino">Polyomino</a>

%F a(n) = A001168(2*n).

%t A001168 = Cases[Import["https://oeis.org/A001168/b001168.txt", "Table"], {_, _}][[All, 2]];

%t a[n_] := A001168[[2 n]];

%t a /@ Range[1, Length[A001168]/2 // Floor] (* _Jean-François Alcover_, Sep 22 2019 *)

%Y Bisection of A001168.

%Y Cf. A210987, A210988, A210996,

%K nonn

%O 1,1

%A _Omar E. Pol_, Sep 16 2012