A305540 → θ+1

nonnegative coefficients

Proved for all n all roots real, in (−∞, 0]coefficients of one sign Hadamard kernel

Recurrence

\(P_{n}(x) = \left(-2\,x^{2}\right)\,P_{n-4}(x) + \left(-x^{2} - x^{3}\right)\,P_{n-4}'(x) + \left(1 + 4\,x\right)\,P_{n-2}(x) + \left(x + x^{2}\right)\,P_{n-2}'(x)\)

\(P_{0}(x) = 1\)

\(P_{1}(x) = 1 + 2\,x\)

\(P_{2}(x) = 1 + 4\,x\)

\(P_{3}(x) = 1 + 8\,x + 9\,x^{2}\)

Rows ?

n	x⁰	x¹	x²	x³	x⁴	x⁵	x⁶	x⁷	P_n(1)
0	1								1
1	1	2							3
2	1	4							5
3	1	8	9						18
4	1	12	18						31
5	1	20	63	48					132
6	1	28	108	96					233
7	1	44	279	528	300				1152
8	1	60	450	960	600				2071
9	1	92	1035	3600	4800	2160			11688
10	1	124	1620	6240	9000	4320			21305
11	1	188	3519	19920	46500	47520	17640		135288
12	1	252	5418	33600	84000	90720	35280		249271
13	1	380	11403	98448	357000	619920	511560	161280	1759992
14	1	508	17388	163296	630000	1149120	987840	322560	3270713

Technical details

Node id: n-50db7487a36f0f5e · revision 0 · JSON
Definition source: derived:theta_plus_one
Fingerprint: f6-01f0bf82962cd518

Observed on the stored rows ?

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

Matches ?

No OEIS matches.

Submission text ?

Atlas rows n = 0, …, ascending powers of x

%e Example

Triangle begins:
  0: 1;
  1: 1,  2;
  2: 1,  4;
  3: 1,  8,    9;
  4: 1, 12,   18;
  5: 1, 20,   63,   48;
  6: 1, 28,  108,   96;
  7: 1, 44,  279,  528,  300;
  8: 1, 60,  450,  960,  600;
  9: 1, 92, 1035, 3600, 4800, 2160;

%F Formula

The row polynomials satisfy P(n,x) = -2*x^2*P(n-4,x) - (x^2+x^3)*d/dx P(n-4,x) + (1+4*x)*P(n-2,x) + (x+x^2)*d/dx P(n-2,x) for n >= 4, with P(0,x) = 1, P(1,x) = 1 + 2*x, P(2,x) = 1 + 4*x, P(3,x) = 1 + 8*x + 9*x^2.

%t Mathematica

P[0, x_] := 1;
P[1, x_] := 1 + 2*x;
P[2, x_] := 1 + 4*x;
P[3, x_] := 1 + 8*x + 9*x^2;
P[n_, x_] := P[n, x] = Expand[-2*x^2*P[n - 4, x] - (x^2 + x^3)*D[P[n - 4, x], x] + (1 + 4*x)*P[n - 2, x] + (x + x^2)*D[P[n - 2, x], x]];
Table[CoefficientList[P[n, x], x], {n, 0, 9}] // Flatten

%o PARI/GP

P(N) = {my(v = vector(N + 1)); v[1] = 1; v[2] = 1 + 2*x; v[3] = 1 + 4*x; v[4] = 1 + 8*x + 9*x^2; for(n = 4, N, my(i = n + 1); v[i] = -2*x^2*v[i - 4] - (x^2 + x^3)*deriv(v[i - 4], x) + (1 + 4*x)*v[i - 2] + (x + x^2)*deriv(v[i - 2], x)); v};
row(n, p) = {my(c = Vecrev(p)); c};
T(N) = {my(v = P(N)); concat(vector(#v, i, row(i - 1, v[i])))};
T(9)

polytool c48629374597

Properties

Real-rooted? Every row P_n, n ≥ 0, is zero or real-rooted with all roots in (−∞, 0]
by Laguerre’s theorem on multiplier sequences
Coefficients of one sign? Every nonzero row, n ≥ 0: the coefficients of P_n have one sign
derived from Laguerre’s theorem on multiplier sequences
Hadamard kernel (Malo)? Rows P_n, n ≥ 0, are Hadamard kernels (preserve real-rootedness)
derived from Laguerre’s theorem on multiplier sequences

Proof chains ? JSON

Laguerre’s theorem on multiplier sequences [SP14; Bra15, Thm 7.1 of arXiv:1410.6601] polytool ? step ›
- from Triangle read by rows: T(n,k) is the number of achiral loops (necklaces or bracelets) of length n using exactly k diffe…?
  - Iterated real-rootedness preservers [SP14; Bra15, Thm 7.1 of arXiv:1410.6601; Bra06, Cor 3.5] polytool ? step › direct check

References

[Bra06] Petter Brändén. On linear transformations preserving the Pólya frequency property. Transactions of the American Mathematical Society, 358(8):3697–3716, February 2006. doi:10.1090/s0002-9947-06-03856-6
[Bra15] Petter Brändén. Unimodality, log-concavity, real-rootedness and beyond. Handbook of enumerative combinatorics, :437–483, March 2015. doi:10.1201/b18255-10
[SP14] J Schur and G Polya. Über zwei Arten von Faktorenfolgen in der Theorie der algebraischen Gleichungen. J. Reine Angew. Math., 1914.