OFFSET
0,3
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..1000
E. Bannai, S. T. Dougherty, M. Harada and M. Oura, Type II Codes, Even Unimodular Lattices and Invariant Rings, IEEE Trans. Information Theory, Volume 45, Number 4, 1999, 1194-1205.
Index entries for linear recurrences with constant coefficients, signature (2,-1,2,-4,2,-1,2,-1).
FORMULA
G.f. ( 1-x+3*x^2+6*x^3+5*x^5+2*x^6 ) / ( (1+x+x^2)^2*(x-1)^4 ). - R. J. Mathar, Oct 01 2011
a(0)=1, a(1)=1, a(2)=4, a(3)=15, a(4)=24, a(5)=44, a(6)=81, a(7)=115, a(n)= 2*a(n-1)- a(n-2)+2*a(n-3)-4*a(n-4)+2*a(n-5)-a(n-6)+2*a(n-7)-a(n-8). - Harvey P. Dale, Jan 12 2013
a(n) ~ 8/27*n^3. - Ralf Stephan, May 17 2014
MAPLE
(1+2*x^2+9*x^3+6*x^4+5*x^5+7*x^6+2*x^7)/((1-x)*(1-x^2)*(1-x^3)^2);
MATHEMATICA
CoefficientList[Series[(1-x+3x^2+6x^3+5x^5+2x^6)/((1+x+x^2)^2(x-1)^4), {x, 0, 50}], x] (* or *) LinearRecurrence[{2, -1, 2, -4, 2, -1, 2, -1}, {1, 1, 4, 15, 24, 44, 81, 115}, 50] (* Harvey P. Dale, Jan 12 2013 *)
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
STATUS
approved