Real-rooted atlas

A108299: Triangle read by rows, 0 <= k <= n: T(n,k) = binomial(n-[(k+1)/2],[k/2])*(-1)^[(k+1)/2].

A108299

Proved for all n: all roots real what this means

Recurrence from OEIS A108299
\(P_{n}(x) = \left(1\right)\,P_{n-1}(x) + \left(-x^{2}\right)\,P_{n-2}(x)\)
\(P_{1}(x) = 1\)
\(P_{2}(x) = 1 - x\)

Rows ?

nx0x1x2x3x4x5x6x7Pn(1)
111
21-10
31-1-1-1
41-1-21-1
51-1-3210
61-1-433-11
71-1-546-3-11
81-1-6510-6-410

Show all 15 stored rows

Generated b-files: A108299, A130777 (reversed triangle) ?

Computed in your browser ?

Technical details
Node id
n-c1c65e1c83bcd2f2 · revision 1 · JSON
Definition source
oeis_catalog:A108299
Fingerprint
f6-932b52f52bd35d70

Observed on the stored rows ?

  • Degrees: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 (affine: slope 1, intercept -1)
  • Palindromic rows: no
  • γ-positive (gamma_positive): no
  • Nonnegative coefficients (nonn): no
  • Only rational roots (rr_by_factors: every nonzero row is a product of linear factors over ℚ): no

OEIS matches ?

A generated b-file is computed from the node's definition along the row alignment of its OEIS link and starts at the entry's offset. It is an identification on a finite prefix, not a proof that the node and the OEIS entry agree for every n.

OEIS submission text ?

Fields to paste into an OEIS submission: the example %e, the formula %F and programs %t (Mathematica) and %o (PARI/GP) that list the same rows. For an OEIS link the row numbers, the offset and the orientation are those of the entry, as matched; the matched terms were compared with the published ones, which identifies the node with the entry on a finite prefix, not for every n. The PARI/GP program is not machine-checked here.

The atlas's own rows: n = 1, …, ascending powers of x
%e Example
Triangle begins:
   1: 1;
   2: 1, -1;
   3: 1, -1, -1;
   4: 1, -1, -2, 1;
   5: 1, -1, -3, 2,  1;
   6: 1, -1, -4, 3,  3,  -1;
   7: 1, -1, -5, 4,  6,  -3,  -1;
   8: 1, -1, -6, 5, 10,  -6,  -4,  1;
   9: 1, -1, -7, 6, 15, -10, -10,  4, 1;
  10: 1, -1, -8, 7, 21, -15, -20, 10, 5, -1;
%F Formula
The row polynomials satisfy P(n,x) = P(n-1,x) - x^2*P(n-2,x) for n >= 3, with P(1,x) = 1, P(2,x) = 1 - x.
%t Mathematica
P[1, x_] := 1;
P[2, x_] := 1 - x;
P[n_, x_] := P[n, x] = Expand[P[n - 1, x] - x^2*P[n - 2, x]];
Table[CoefficientList[P[n, x], x], {n, 1, 10}] // Flatten
%o PARI/GP
P(N) = {my(v = vector(N)); v[1] = 1; v[2] = 1 - x; for(n = 3, N, my(i = n); v[i] = v[i - 1] - x^2*v[i - 2]); v};
row(n, p) = {my(c = Vecrev(p)); c};
T(N) = {my(v = P(N)); concat(vector(#v, i, row(i, v[i])))};
T(10)

Generated with polytool c48629374597.

A108299: triangle, offset 0, from the row P1
%e Example
Triangle begins:
  0: 1;
  1: 1, -1;
  2: 1, -1, -1;
  3: 1, -1, -2, 1;
  4: 1, -1, -3, 2,  1;
  5: 1, -1, -4, 3,  3,  -1;
  6: 1, -1, -5, 4,  6,  -3,  -1;
  7: 1, -1, -6, 5, 10,  -6,  -4,  1;
  8: 1, -1, -7, 6, 15, -10, -10,  4, 1;
  9: 1, -1, -8, 7, 21, -15, -20, 10, 5, -1;
%F Formula
The row polynomials satisfy P(n,x) = P(n-1,x) - x^2*P(n-2,x) for n >= 2, with P(0,x) = 1, P(1,x) = 1 - x.
%t Mathematica
P[0, x_] := 1;
P[1, x_] := 1 - x;
P[n_, x_] := P[n, x] = Expand[P[n - 1, x] - x^2*P[n - 2, x]];
Table[PadRight[CoefficientList[P[n, x], x], n + 1], {n, 0, 9}] // Flatten
%o PARI/GP
P(N) = {my(v = vector(N + 1)); v[1] = 1; v[2] = 1 - x; for(n = 2, N, my(i = n + 1); v[i] = v[i - 1] - x^2*v[i - 2]); v};
row(n, p) = {my(c = Vecrev(p)); c = concat(c, vector(n + 1 - #c)); c};
T(N) = {my(v = P(N)); concat(vector(#v, i, row(i - 1, v[i])))};
T(9)

Generated with polytool c48629374597.

A130777: reversed triangle, offset 0, from the row P1
%e Example
Triangle begins:
  0:  1;
  1: -1,  1;
  2: -1, -1,   1;
  3:  1, -2,  -1,   1;
  4:  1,  2,  -3,  -1,   1;
  5: -1,  3,   3,  -4,  -1,  1;
  6: -1, -3,   6,   4,  -5, -1,  1;
  7:  1, -4,  -6,  10,   5, -6, -1,  1;
  8:  1,  4, -10, -10,  15,  6, -7, -1,  1;
  9: -1,  5,  10, -20, -15, 21,  7, -8, -1, 1;
%F Formula
Row n lists the coefficients of P(n,x) in descending powers of x, where P(n,x) = P(n-1,x) - x^2*P(n-2,x) for n >= 2, with P(0,x) = 1, P(1,x) = 1 - x.
%t Mathematica
P[0, x_] := 1;
P[1, x_] := 1 - x;
P[n_, x_] := P[n, x] = Expand[P[n - 1, x] - x^2*P[n - 2, x]];
Table[Reverse[PadRight[CoefficientList[P[n, x], x], n + 1]], {n, 0, 9}] // Flatten
%o PARI/GP
P(N) = {my(v = vector(N + 1)); v[1] = 1; v[2] = 1 - x; for(n = 2, N, my(i = n + 1); v[i] = v[i - 1] - x^2*v[i - 2]); v};
row(n, p) = {my(c = Vecrev(p)); c = concat(c, vector(n + 1 - #c)); c = Vecrev(c); c};
T(N) = {my(v = P(N)); concat(vector(#v, i, row(i - 1, v[i])))};
T(9)

Generated with polytool c48629374597.

Proved properties

  • Real-rooted. Every row P_n, n >= 1, is zero or real-rooted with all roots in (-inf, +inf)
    Every polynomial of the sequence has only real roots, inside the stated interval.
    by the cited steps: e-7467667c9a732a94

Proof chains

1 incoming proof step. Each step is expanded back to the roots of the proof DAG, the theorem checks of a node's own rule. JSON

Used in 3 proof steps

No candidate equalities or related sequences.

References

  1. [Fav35] Jean Favard. Sur les polynômes de tchebicheff. C. R. Acad. Sci. Paris, 200:2052–2053, 1935.
  2. [Sze39] G. Szegő. Orthogonal Polynomials. Colloquium publications, American Mathematical Society, 1939. doi:10.1090/coll/023