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A120803 Number of series-reduced balanced trees with n leaves. 17

%I #14 Oct 26 2018 00:51:31

%S 1,1,1,2,2,4,4,8,9,16,20,37,47,80,111,183,256,413,591,940,1373,2159,

%T 3214,5067,7649,12054,18488,29203,45237,71566,111658,176710,276870,

%U 437820,687354,1085577,1705080,2688285,4221333,6644088,10425748

%N Number of series-reduced balanced trees with n leaves.

%C In other words, rooted trees with all leaves at the same level and no node having exactly one child; the order of children is not significant.

%H Alois P. Heinz, <a href="/A120803/b120803.txt">Table of n, a(n) for n = 1..1000</a>

%F Let s_0(n) = 1 if n = 1, 0 otherwise; s_{k+1}(n) = EULER(s_k)(n) - s_k(n), where EULER is the Euler transform. Then a_n = sum_k s_k(n). (s_k(n) is the number of such trees of height k.) Note that s_k(n) = 0 for n < 2^k.

%e From _Gus Wiseman_, Oct 07 2018: (Start)

%e The a(10) = 16 series-reduced balanced rooted trees:

%e (oooooooooo)

%e ((ooooo)(ooooo))

%e ((oooo)(oooooo))

%e ((ooo)(ooooooo))

%e ((oo)(oooooooo))

%e ((ooo)(ooo)(oooo))

%e ((oo)(oooo)(oooo))

%e ((oo)(ooo)(ooooo))

%e ((oo)(oo)(oooooo))

%e ((oo)(oo)(ooo)(ooo))

%e ((oo)(oo)(oo)(oooo))

%e ((oo)(oo)(oo)(oo)(oo))

%e (((oo)(ooo))((oo)(ooo)))

%e (((oo)(oo))((ooo)(ooo)))

%e (((oo)(oo))((oo)(oooo)))

%e (((oo)(oo))((oo)(oo)(oo)))

%e (End)

%o (PARI) EulerT(v)={Vec(exp(x*Ser(dirmul(v,vector(#v,n,1/n))))-1, -#v)}

%o seq(n)={my(u=vector(n), v=vector(n)); u[1]=1; while(u, v+=u; u=EulerT(u)-u); v} \\ _Andrew Howroyd_, Oct 26 2018

%Y Cf. A000081, A000669, A001003, A001678, A007059, A048816, A079500, A119262, A244925, A316624, A320154, A320160, A320169, A320179.

%K nonn

%O 1,4

%A _Franklin T. Adams-Watters_, Aug 18 2006

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Last modified March 28 09:04 EDT 2024. Contains 371240 sequences. (Running on oeis4.)