OFFSET
0,2
LINKS
Colin Barker, Table of n, a(n) for n = 0..1000
Jean-Guillaume Eon, Algebraic determination of generating functions for coordination sequences in crystal structures, Acta Cryst. A58 (2002), 47-53.
Index entries for linear recurrences with constant coefficients, signature (0,3,0,-3,0,1).
FORMULA
G.f.: (1 + 2*x + 7*x^2 + 4*x^3 + 19*x^4 + 2*x^5 - 3*x^6) / (1 - x^2)^3.
From Colin Barker, Feb 13 2018: (Start)
a(n) = 3*n^2 - 2 for n>0 and even.
a(n) = n^2 + 1 for n odd.
a(n) = 3*a(n-2) - 3*a(n-4) + a(n-6) for n>6.
(End)
PROG
(PARI) Vec((1 + 2*x + 7*x^2 + 4*x^3 + 19*x^4 + 2*x^5 - 3*x^6) / ((1 - x)^3*(1 + x)^3) + O(x^60)) \\ Colin Barker, Feb 13 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Dec 24 2001
STATUS
approved