OFFSET
0,3
COMMENTS
From Wolfdieter Lang, Oct 02 2013: (Start)
These numbers a(n) and those of A030191(n) =: b(n), both interspersed with zeros, appear in the formula for nonnegative powers of the algebraic number rho(10) := 2*cos(pi/10) = phi*sqrt(3-phi), with the golden section phi, in terms of the power basis of the number field Q(rho(10)) of degree 4 (see A187360, n=10). In a (regular) decagon rho(10) is the length ratio of a smallest diagonal to the side. rho(10)^n = sum(A(n,k)*rho(10)^k, k=0..3), with A(2*k+1,0) = 0, A(2*k,0) = a(k), k >= 0; A(2*k,1) = 0, A(2*k+1,1) = a(k), k >= 0; A(2*k+1,2) = 0, k >= 0, A(0,2) = 0, A(2*k,2) = b(k-1), k >= 1; and A(2*k,3) = 0, k >= 0, A(1,3) = 0, A(2*k+1,3) = b(k-1), k >= 1. (End)
LINKS
FORMULA
G.f.: (1-5x)/(1-5x+5x^2).
From Wolfdieter Lang, Oct 02 2013: (Start)
a(n) = b(n) - 5*b(n-1), n >= 0, with b(n) = A030191(n) = (sqrt(5))^n*S(n, sqrt(5)), with Chebyshev S-polynomials (see A049310).
a(n) = 5*(a(n-1) - a(n-2)), n >= 1, a(-1) = 1 = a(0). (End)
EXAMPLE
Powers of rho(10) in the Q(rho(10)) power basis for n = 5: rho(10)^5 = 0*1 + a(2)*rho(10) + 0*rho(10)^2 + b(1)*rho(10)^3 = -5*rho(10) + 5*rho(10)^3. - Wolfdieter Lang, Oct 02 2013
MATHEMATICA
LinearRecurrence[{5, -5}, {1, 0}, 40] (* Harvey P. Dale, Dec 08 2015 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Creighton Dement, Sep 23 2004
EXTENSIONS
More terms from David Wasserman, Jan 16 2008
STATUS
approved