|
%I #9 Mar 31 2012 10:23:11
%S 1,4,18,83,385,1788,8305,38575,179170,832189,3865253,17952864,
%T 83385309,387298083,1798875698,8355202169,38807241321,180247221864,
%U 837190686169,3888482927823,18060759310562,83886449530197,389625723579965
%N Number of row-convex polyplets with n cells.
%C Equivalent to a sequence of row-convex polyhexes (A059716).
%F G.f.: -((x(x-1)^3)/(1-7x+13x^2-10x^3+2x^4)).
%F a(n) = 7a(n-1)-13a(n-2)+10a(n-3)-2a(n-4) for n > 4.
%e a(3) = 18 = A006770(3)-2 omits the two 3-plets with non-convex rows (V and inverted V).
%t a[n_]:={1,4,18,83}[[n]]/;n<5; a[n_]:=a[n]=7a[n-1]-13a[n-2]+10a[n-3]-2a[n-4]; Array[a, 23]
%Y Cf. A006770 (all fixed polyplets); A059716 (row-convex polyhexes); A001169 (row-convex polyominoes).
%K nonn
%O 1,2
%A _David Bevan_, Mar 03 2011
|
