OFFSET
0,2
COMMENTS
Second convolution of A010892.
a(n) equals the coefficient of x^2 of the characteristic polynomial of the (n+2)X(n+2) tridiagonal matrix with 1's along the main diagonal, the superdiagonal, and the subdiagonal (see Mathematica code below). [John M. Campbell, Jul 10 2011]
FORMULA
a(n)=sum( A128503(n,m),m=0..floor(n/2)), n>=0.
G.f.: 1/(1-x+x^2)^3.
a(n) = (floor(n/3)+1)*(floor(n/3)-floor((n-1)/3)+(3/2)*(floor(n/3)+2)*(3*floor((n+1)/3)-n))*(-1)^n. - Tani Akinari, Jul 03 2013
MATHEMATICA
Table[Coefficient[CharacteristicPolynomial[Array[KroneckerDelta[#1, #2] + KroneckerDelta[#1, #2 - 1] + KroneckerDelta[#1, #2 + 1] &, {n + 2, n + 2}], x], x^2], {n, 0, 70}] (* John M. Campbell, Jul 10 2011 *)
PROG
(PARI) Vec(1/(1-x+x^2)^3+O(x^66)) \\ Joerg Arndt, Jul 02 2013
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Wolfdieter Lang Apr 04 2007
STATUS
approved