OFFSET
1,1
COMMENTS
Here m=(11*(2*n-1)-9*(-1)^n)/4 for n>0.
(18*m^2 + 1)/11 is integer for m=5+11k and m=6+11k, k=0,1,2,.... [ Corrected by Bruno Berselli, Jun 28 2010]
LINKS
B. Berselli, Table of n, a(n) for n = 1..10000.
Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).
FORMULA
Contribution from Bruno Berselli, Jun 29 2010: (Start)
G.f.: x*(41+18*x+278*x^2+18*x^3+41*x^4)/((1+x)^2*(1-x)^3).
a(n) = a(-n+1) = a(n-1)+2*a(n-2)-2*a(n-3)-a(n-4)+a(n-5).
a(n) = (198*n*(n-1)-81*(2*n-1)*(-1)^n+83)/4. (End)
PROG
(PARI) a(n)=(198*n*(n-1)-81*(2*n-1)*(-1)^n+83)/4 \\ Charles R Greathouse IV, Oct 07 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Zak Seidov, Jan 08 2006
EXTENSIONS
Definition corrected, comment and cross-reference added by Bruno Berselli, Jul 13 2010
STATUS
approved