A187077 - OEIS

%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