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 A133107 Number of Ferrers diagrams with a single strictly smaller Ferrers puncture with the same orientation removed from the top with half-perimeter = n. 2

%I

%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

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Last modified September 19 21:11 EDT 2021. Contains 347564 sequences. (Running on oeis4.)