login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A321966 Triangle read by rows, coefficients of a family of orthogonal polynomials, T(n, k) for 0 <= k <= n. 3
1, 1, 1, 2, 5, 1, 6, 27, 12, 1, 24, 168, 123, 22, 1, 120, 1200, 1275, 365, 35, 1, 720, 9720, 13950, 5655, 855, 51, 1, 5040, 88200, 163170, 87465, 18480, 1722, 70, 1, 40320, 887040, 2046240, 1387680, 383145, 49476, 3122, 92, 1 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

0,4

COMMENTS

The polynomials represent a family of orthogonal polynomials which obey a recurrence of the form p(n, x) = (x + alpha(n))*p(n-1, x) - beta(n)*p(n-2, x) + gamma(n)*p(n-3, x). For the details see the Maple program.

We conjecture that the polynomials have only negative and simple real roots.

LINKS

Table of n, a(n) for n=0..44.

Peter Luschny, Plot of the polynomials

FORMULA

Let R be the inverse of the Riordan square [see A321620] of (1 - 2*x)^(-1/2) then T(n, k) = (-1)^(n-k)*R(n, k).

EXAMPLE

p(0,x) = 1;

p(1,x) = x + 1;

p(2,x) = x^2 + 5*x + 2;

p(3,x) = x^3 + 12*x^2 + 27*x + 6;

p(4,x) = x^4 + 22*x^3 + 123*x^2 + 168*x + 24;

p(5,x) = x^5 + 35*x^4 + 365*x^3 + 1275*x^2 + 1200*x + 120;

p(6,x) = x^6 + 51*x^5 + 855*x^4 + 5655*x^3 + 13950*x^2 + 9720*x + 720;

MAPLE

P := proc(n) option remember; local a, b, c;

a := n -> 3*n-2; b := n -> (n-1)*(3*n-4); c := n -> (n-2)^2*(n-1);

if n = 0 then return 1 fi;

if n = 1 then return x + 1 fi;

if n = 2 then return x^2 + 5*x + 2 fi;

expand((x+a(n))*P(n-1) - b(n)*P(n-2) + c(n)*P(n-3)) end:

seq(print(P(n)), n=0..6); # Computes the polynomials.

MATHEMATICA

a[n_] := 3n-2; b[n_] := (n-1)(3n-4); c[n_] := (n-2)^2 (n-1);

P[n_] := P[n] = Switch[n, 0, 1, 1, x+1, 2, x^2 + 5x + 2, _, Expand[(x+a[n]) P[n-1] - b[n] P[n-2] + c[n] P[n-3]]];

Table[CoefficientList[P[n], x], {n, 0, 8}] // Flatten (* Jean-Fran├žois Alcover, Jan 01 2019, from Maple *)

PROG

(Sage) # uses[RiordanSquare from A321620]

R = RiordanSquare((1 - 2*x)^(-1/2), 9, True).inverse()

for n in (0..8): print([(-1)^(n-k)*c for (k, c) in enumerate(R.row(n)[:n+1])])

CROSSREFS

p(n, 1) = A321965(n); p(n, 0) = n! = A000142(n).

Cf. A321620.

Sequence in context: A174232 A065224 A325137 * A304822 A165278 A106619

Adjacent sequences:  A321963 A321964 A321965 * A321967 A321968 A321969

KEYWORD

nonn,tabl

AUTHOR

Peter Luschny, Dec 20 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified April 7 09:13 EDT 2020. Contains 333300 sequences. (Running on oeis4.)