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Number of fixed points in range [A014137(n-1)..A014138(n-1)] of permutations A127377/A127378 and A127387.
5

%I #5 Mar 31 2012 13:21:14

%S 1,1,0,1,2,4,10,23,56,138,344,870,2220,5716,14828,38717,101682,268416,

%T 711810,1895432,5066030,13586082,36547534,98593064,266661162,

%U 722953814,1964358938,5348367006,14589803090,39870312218,109136843138

%N Number of fixed points in range [A014137(n-1)..A014138(n-1)] of permutations A127377/A127378 and A127387.

%F G.f. satisfies: A(x) = (1 + x*A(x)^2)*(1+x)/(1+x+2*x^2).

%o (PARI) {a(n)=local(A=1+x+x*O(x^n));for(i=0,n,A=(1 + x*A^2)*(1+x)/(1+x+2*x^2));polcoeff(A,n)}

%Y This is INVERTi transform of A086625 (appropriately shifted). I.e. INVERT([1, 1, 0, 1, 2, 4, 10, 23, 56, 138, 344, 870, 2220, 5716]) gives: 1, 2, 3, 6, 12, 26, 59, 138, 332, 814, 2028, 5118, ... (beginning of A086625)

%K nonn

%O 0,5

%A _Antti Karttunen_, Jan 16 2007. Generating function, PARI-program and most of the terms supplied by _Paul D. Hanna_, Jan 15 2007.