Sequence-Counting Sequences: Variants of A008934
Paul D. Hanna
pauldhanna at juno.com
Sat Sep 17 09:45:23 CEST 2005
Seqfans,
Would someone wish to extend the following sequence-counting
sequences?
For positive integer values of m, they are defined by:
"Number of sequences (a_1, a_2,..., a_n) with a_1 = 1
such that a_i < a_{i+1} <= m*a_i for all i."
For m=3:
"Number of sequences (a_1, a_2,..., a_n) with a_1 = 1
such that a_i < a_{i+1} <= 3*a_i for all i."
I get:
1,2,10,114,2970,182402,27392682,
An example of the tree being enumerated for m=3 is:
1
| \
2 3
| \ \ \ \ \ \ \ \ \
3,4,5,6 4,5,6,7,8,9
etc. ...
-------------------------------------------------------
For m=4:
"Number of sequences (a_1, a_2,..., a_n) with a_1 = 1
such that a_i < a_{i+1} <= 4*a_i for all i."
I get:
1,3,27,693,52812,12628008,
-------------------------------------------------------
For m=5:
"Number of sequences (a_1, a_2,..., a_n) with a_1 = 1
such that a_i < a_{i+1} <= 5*a_i for all i."
I get:
1,4,56,2704,481376,337587520,
-------------------------------------------------------
These sequences are obvious variants of A008934 (where m=2):
"Number of tournament sequences: sequences (a_1, a_2, ..., a_n) with
a_1 = 1 such that a_i < a_{i+1} <= 2*a_i for all i."
which begins:
1,1,2,7,41,397,6377,171886,7892642,627340987,87635138366,
21808110976027,9780286524758582,7981750158298108606,
11950197013167283686587,33046443615914736611839942
Reference (Cook and Kleber) for A008934:
http://www.combinatorics.org/Volume_7/PDF/v7i1r44.pdf
which supplies a formula for A008934.
See formula in the associated table (with A008934 as column 1):
http://www.research.att.com/projects/OEIS?Anum=A093729
Can the formula be extended for m>2?
Finding more terms seems very time-consuming without the use
of some derived formula.
Thanks,
Paul
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