OFFSET
1,2
COMMENTS
See A192232.
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (2,2,2,-1).
FORMULA
Empirical G.f.: x^2*(3-x)*(1+x)/(1-2*x-2*x^2-2*x^3+x^4). - Colin Barker, Sep 11 2012
MATHEMATICA
q[x_]:= x + 1;
reductionRules = {x^y_?EvenQ -> q[x]^(y/2), x^y_?OddQ -> x q[x]^((y - 1)/2)};
t = Table[Last[Most[FixedPointList[Expand[#1 /. reductionRules] &, ChebyshevU[n, x]]]], {n, 1, 40}];
Table[Coefficient[Part[t, n], x, 0], {n, 1, 40}] (* A192235 *)
Table[Coefficient[Part[t, n], x, 1], {n, 1, 40}] (* A192236 *)
Table[Coefficient[Part[t, n]/2, x, 1], {n, 1, 40}] (* A192237 *)
(* by Peter J. C. Moses, Jun 25 2011 *)
LinearRecurrence[{2, 2, 2, -1}, {0, 3, 8, 21}, 40] (* G. C. Greubel, Jul 30 2019 *)
PROG
(PARI) a(n)=my(t=polchebyshev(n, 2)); while(poldegree(t)>1, t=substpol(t, x^2, x+1)); subst(t, x, 0) \\ Charles R Greathouse IV, Feb 09 2012
(PARI) m=40; v=concat([0, 3, 8, 21], vector(m-4)); for(n=5, m, v[n] = 2*v[n-1]+2*v[n-2]+2*v[n-3]-v[n-4]); v \\ G. C. Greubel, Jul 30 2019
(Magma) I:=[0, 3, 8, 21]; [n le 4 select I[n] else 2*Self(n-1) +2*Self(n-2) +2*Self(n-3) -Self(n-4): n in [1..40]]; // G. C. Greubel, Jul 30 2019
(Sage)
@cached_function
def a(n):
if (n==0): return 0
elif (1 <= n <= 3): return fibonacci(2*n+2)
else: return 2*(a(n-1) + a(n-2) + a(n-3)) - a(n-4)
[a(n) for n in (0..40)] # G. C. Greubel, Jul 30 2019
(GAP) a:=[0, 3, 8, 21];; for n in [5..40] do a[n]:=2*a[n-1]+2*a[n-2]+ 2*a[n-3]-a[n-4]; od; a; # G. C. Greubel, Jul 30 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Clark Kimberling, Jun 26 2011
STATUS
approved