OFFSET
0,2
LINKS
FORMULA
abs(a(n)) = 2^A047267(n).
a(n) = 2*4^n(cos(Pi*(n+1)/3) - sqrt(3)*sin(Pi*(n+1))/3).
a(n) = 4^n*Sum_{k=0..n} A121314(n,k)*(-1)^k*3^(n-k). - Philippe Deléham, Nov 01 2008
a(n) = A128018(n)*2^n. - Philippe Deléham, Nov 14 2008
a(n) = 4*a(n-1) - 16*a(n-2); a(0)=1, a(1)=-4. - Harvey P. Dale, Sep 30 2014
From Amiram Eldar, Jan 25 2026: (Start)
Sum_{n>=0} 1/a(n) = 46/65.
Sum_{n>=0} (-1)^n/a(n) = 26/21. (End)
MATHEMATICA
CoefficientList[Series[(1-8x)/(1-4x+16x^2), {x, 0, 30}], x] (* or *) LinearRecurrence[{4, -16}, {1, -4}, 30] (* Harvey P. Dale, Sep 30 2014 *)
CROSSREFS
KEYWORD
easy,sign
AUTHOR
Paul Barry, Mar 15 2008
EXTENSIONS
More terms from Amiram Eldar, Jan 25 2026
STATUS
approved