OFFSET
1,2
LINKS
Index entries for linear recurrences with constant coefficients, signature (19,-19,1).
FORMULA
a(n+1) = 9*a(n+1)+4+(80*a(n)^2+80*a(n)+25)^0.5.
G.f.: f(z)=a(0)+a(1)*z+a(2)*z^2+...=(9*z-z^2)/((1-z)*(1-18*z+z^2))
a(n) = ((sqrt(5)+2)/8)*(9+4*sqrt(5))^n+((-sqrt(5)+2)/8)*(9-4*sqrt(5))^n-0.5 [From Richard Choulet, Nov 26 2008]
a(n) = (Lucas(6*n-3)-4)/8, where Lucas=A000032(n). [Gary Detlefs, Dec 07 2010]
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Richard Choulet, Aug 30 2007, Oct 09 2007
STATUS
approved