%I #7 Mar 08 2015 21:00:51
%S 1,7,32,121,410,1294,3888,11273,31826,88041,239734,644758,1717191,
%T 4538129,11919760,31156313,81125827,210604604,545462798,1410226551,
%U 3641097828,9391872711,24208902420,62373915102,160663604377
%N Number of Ferrers diagrams with a single strictly smaller Ferrers puncture with the same orientation removed from the top with half-perimeter = n.
%H Arvind Ayyer, Sep 11 2007, <a href="/A133107/b133107.txt">Table of n, a(n) for n = 6..76</a>
%F G.f.: x^2*(-1 + 3*x - x^2 + (5*x^4 - 6*x^3 + 11*x^2 - 6*x + 1 + 4*x^6 - 12*x^5)^(1/2))/(2*(x^2 - 3*x + 1)*(1-2*x)^2)
%e The sequence starts with n=6 because the smallest such object whose illustration is below has a perimeter of 12. (1 denotes cell inside the Ferrers diagram.)
%e 1 1
%e 111
%Y Cf. A057410, A057406, A133106.
%K easy,nonn
%O 6,2
%A _Arvind Ayyer_, Sep 11 2007
|