OFFSET
0,3
COMMENTS
Vertex number of a square spiral similar to A118277.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).
FORMULA
a(n) = (3*(-1+(-1)^n)+2*(5+(-1)^n)*n+14*n^2)/16. a(n) = a(n-1)+2*a(n-2)-2*a(n-3)-a(n-4)+a(n-5). G.f.: -x*(2*x^2+4*x+1) / ((x-1)^3*(x+1)^2). - Colin Barker, Sep 15 2013
PROG
(PARI) Vec(-x*(2*x^2+4*x+1)/((x-1)^3*(x+1)^2) + O(x^100)) \\ Colin Barker, Sep 15 2013
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Omar E. Pol, Aug 03 2012
EXTENSIONS
More terms from Colin Barker, Sep 15 2013
STATUS
approved