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Lucas Polynomial


LucasPolynomial

The Lucas polynomials are the w-polynomials obtained by setting p(x)=x and q(x)=1 in the Lucas polynomial sequence. For a nonnegative integer n, they are given explicitly by

 L_n(x)=2^(-n)[(x-sqrt(x^2+4))^n+(x+sqrt(x^2+4))^n].
(1)

Thus L_0(x)=2. The first few with n>0 are

L_1(x)=x
(2)
L_2(x)=x^2+2
(3)
L_3(x)=x^3+3x
(4)
L_4(x)=x^4+4x^2+2
(5)
L_5(x)=x^5+5x^3+5x
(6)

(OEIS A114525).

The Lucas polynomial is implemented in the Wolfram Language as LucasL[n, x].

The Lucas polynomial has generating function

G(x,t)=(2-xt)/(1-t^2-tx)
(7)
=sum_(n=0)^(infty)L_n(x)t^n
(8)
=2+xt+(x^2+2)t^2+(x^3+3x)t^3+....
(9)

For n>=1, the derivative of L_n(x) satisfies the polynomial identity

 (x^2+4)(dL_n(x))/(dx)=n[xL_n(x)+2L_(n-1)(x)].
(10)

For positive integers m and n, L_n(x) divides L_m(x) iff m is an odd number times n. For an odd prime number p, L_p(x)/x is an irreducible polynomial. For n>=1, the roots of L_n(x) are 2icos[(2k-1)pi/(2n)] for k=1, ..., n. For an odd prime number p, except for the root 0, these roots are 2i times the imaginary part of the roots of the pth cyclotomic polynomial (Koshy 2001, p. 464).

The corresponding W polynomials are called Fibonacci polynomials. The Lucas polynomials satisfy

L_n(0)=1+(-1)^n
(11)
L_n(1)=L_n,
(12)

where the L_ns are Lucas numbers.


See also

Fibonacci Polynomial, Lucas Number, Lucas Polynomial Sequence

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References

Koshy, T. Fibonacci and Lucas Numbers with Applications. New York: Wiley, 2001.Sloane, N. J. A. Sequence A114525 in "The On-Line Encyclopedia of Integer Sequences."

Referenced on Wolfram|Alpha

Lucas Polynomial

Cite this as:

Weisstein, Eric W. "Lucas Polynomial." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/LucasPolynomial.html

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