[seqfan] A new triangle revisited
Ed Jeffery
ed.jeffery at yahoo.com
Tue Dec 6 08:57:23 CET 2011
Seqfans,
On Nov 28, I posted a message about a triangle associated with what
I thought was a new sequence read from the anti-diagonals of a table.
After ignoring the first column it turned out that my table was the same
as A050447 (https://oeis.org/A050447) and its transposed version the
same as A050446 (https://oeis.org/A050446). The table A050447 is
1,1,1,1,1,1,1,...
1,2,3,4,5,6,7,...
1,3,6,10,15,21,28,...
1,5,14,30,55,91,140,...
1,8,31,85,190,371,658,...
I added a comment to A050447 stating some conjectures (which I need
to correct), a few of whichare the following.
Rows of the table:
(iii) The n-th row (n=1,2,...) of the table has generating function of the form
f_n(x) = B_n(x)/(1-x)^n,
in which B_1(x) = B_2(x) = 1 and, for n >= 3, B_n(x) is a polynomial of
degree n-3 in x of the form
B_n(x) = b_0 + b_1*x + ... + b_(n-4)*x^(n-4) + b_(n-3)*x^(n-3)
in which the coefficients b_0, ..., b_(n-3) are given by the (n-2)-th row of
the triangle
T=
1
1,1
1,3,1
1,7,7,1
1,14,31,14,1
1,26,109,109,26,1
etc.
This triangle definitely is not in the OEIS database, and I will submit it
sometime after the holidays since its definition still needs a lot of work.
As an example of its utility, row 8 of the table is the sequence
{1,34,464,2037,8272,26585,72302,173502,377739,...}.
By (iii), f_8(x)=B_8(x)/(1-x)^8, and using row 8-2=6 of the triangle we have
B_8(x)=1+26*x+109*x2+109*x^3+26*x^4+x^5.
Therefore the generating function for row 8 of the table is
f_8(x)=(1+26*x+109*x2+109*x^3+26*x^4+x^5)/(1-x)^8.
Columns of the triangle:
(iv) The second column of the triangle is A001924 shifted to the right one
place, so this column has generating function = x/((1-x-x^2)*(1-x)^2).
(v) However, subsequent columns of the triangle are unknown. In particular,
column 3, which is the sequence {1,7,31,109,...}, has generating function =
x^2*(1-x^2-x^3-x^4+x^5)/((1-2^x-x^2+x^3)*(1-x-x^2)^2*(1-x)^3).(This sequence
I will submit to OEIS as well.)
I can't help but suspect a certain pattern in the denominators of the
generating functions; therefore:
(vi) Generally, for the n-th column of the triangle, the generating function
will be a convolution of the form
x^(n-1)*A_n(x)/(P_n(x)*[P_(n-1)(x)]^2*...*[P_2(x)]^(n-1)*[P_1(x)]^n,
in which A_n(x) and the P_j(x), j in {1,2,...,n}, are polynomials in x, with
P_j(x) being monic, of degree j, and of the form
P_j(x)=c_0*x^j+c_1*x^(j-1)+...+c_(j-1)*x+c_j
in which the coefficients c_0,...,c_j are given by row j of A187660.
What I really need are more terms in the columns of my triangle so I can
at least verify the first few generating functions or, perhaps, discard the
whole idea if I fail. The difficulty for me is that my software can only handle
15-digit numbersin arrays.
Would someone please help me get more terms?
I suspect that from the convolution for the n-th column arises a recurrence
relation requiring knowledge of at most the first s(n) terms (the initial
conditions), where s={1,4,10,20,35,...}=A000292. So, already for column
four. I need more terms.
Finally, I have an idea of how the columns can be generated, if someone
would like to help me.
Thanks,
Ed Jeffery
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