Sub-Fibonacci Tree
Paul D. Hanna
pauldhanna at juno.com
Fri Nov 17 08:55:47 CET 2006
Seqfans,
Here I extend A005270 by one more term and also extend the sequence
a(n) = sum of labels of nodes in generation n in the sub-Fibonacci tree.
I demonstrate a slightly faster method to compute these sequences.
First, I am changing the description to be (hopefully) more clear:
"Sum of labels of nodes in generation n of the sub-Fibonacci tree in
which
a node with label k and parent node with label g, has g child nodes that
are given labels beginning with k+1 through k+g; the tree starts at
generation n=0 with a root node labeled '1' and a child node labeled
'2'."
Would appreciate any suggestions to change in wording.
EXTENDING A005270.
There is a faster way to compute b(n)=A005270(n+1):
b(n) = "number of nodes in generation n of the sub-Fibonacci tree"
by employing the following statistic:
b(n+1) = sum of (parent label)*(label) over all nodes in generation n.
For example,
b(4) = 27 = 3*(4+5);
b(5) = 177 = 4*(5+6+7) + 5*(6+7+8);
b(6) = 1680 = 5*(6+7+8+9) + 6*(7+8+9+10) + 7*(8+9+10+11)+
6*(7+8+9+10+11) + 7*(8+9+10+11+12) + 8*(9+10+11+12+13); ...
Using this method, I extend sequence A005270 by one more term:
1, 1, 1, 1, 2, 6, 27, 177, 1680, 23009, 455368, 13067353,
SUM OF LABELS SEQUENCE.
In like manner, the computation of:
a(n) = "sum of labels of nodes in generation n of the sub-Fibonacci tree"
can be accomplished by the statistic:
a(n+1) = sum of (parent label)*(label) over all nodes in generation n
+ sum of (parent label)*[label*(label+1)/2] over all nodes in generation
n-1.
For example,
a(2) = 3 = 1*2 + 1*( 1*2/2 ) ;
a(3) = 9 = 2*3 + 1*( 2*3/2 ) ;
a(4) = 39 = 3*(4+5) + 2*( 3*4/2 ) ;
a(5) = 252 = 4*(5+6+7) + 5*(6+7+8) + 3*( 4*5/2 + 5*6/2 ) ;
a(6) = 2361 = 5*(6+7+8+9) + 6*(7+8+9+10) + 7*(8+9+10+11) +
6*(7+8+9+10+11) + 7*(8+9+10+11+12) + 8*(9+10+11+12+13) +
4*( 5*6/2 + 6*7/2 + 7*8/2 ) + 5*( 6*7/2 + 7*8/2 + 8*9/2) ;
...
With this method, I extend the sum of labels in generation n to:
1, 2, 3, 9, 39, 252, 2361, 32077, 631058, 18035534,
Would someone please confirm my calculation of the terms:
b(10) = A005270(11) = 13067353 and
a(10) = 18035534
and maybe compute a few more terms?
Thanks,
Paul
----------------------------------------------------
> EXAMPLE.
> The initial nodes of the tree for generations 0..5 are:
> gen 0: [1];
> gen 1: [2];
> gen 2: [3];
> gen 3: [4,5];
> gen 4: (4)->[5,6,7],(5)->[6,7,8];
> gen 5: (5)->[6,7,8,9],(6)->[7,8,9,10],(7)->[8,9,10,11],
> (6)->[7,8,9,10,11],(7)->[8,9,10,11,12],(8)->[9,10,11,12,13];
>
> By definition, there are 2 child nodes for node [3] since
> the parent of node [3] is [2]; likewise,
> there are 3 child nodes for nodes [4] and [5] (in gen.3)
> since the parent of both nodes has label [3] (in gen.2).
>
> Notice the minimum label in generation n is n+1, and
> the maximum label in generation n is Fibonacci(n+2).
>
> From this tree I am interested in gleaning 2 sequences.
>
> SEQUENCE 1.
> I compute the number of nodes in generation n to begin:
> [1, 1, 1, 2, 6, 27, 177, 1680, 23009, 455368, ...]
>
> which is equal (with offset) to A005270:
> "Sub-Fibonacci sequences of length n."
> 1, 1, 1, 1, 2, 6, 27, 177, 1680, 23009, 455368
>
> SEQUENCE 2.
> But the following related sequence is NOT found in the OEIS:
>
> Sum of labels of nodes in generation n:
> [1, 2, 3, 9, 39, 252, 2361, 32077, 631058, ...]
>
> EXTENSION?
> Could someone compute more terms of sequences 1 and 2?
>
> Thanks,
> Paul
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