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A128504 Row sums of array A128503 (second convolution of Chebyshev's S(n,x)=U(n,x/2) polynomials). 3
1, 3, 3, -2, -9, -9, 3, 18, 18, -4, -30, -30, 5, 45, 45, -6, -63, -63, 7, 84, 84, -8, -108, -108, 9, 135, 135, -10, -165, -165, 11, 198, 198, -12, -234, -234, 13, 273, 273, -14, -315, -315, 15, 360, 360, -16, -408, -408, 17, 459, 459 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Second convolution of A010892.

Convolution of A099254 with 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]

LINKS

Table of n, a(n) for n=0..50.

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

Sequence in context: A192787 A214101 A100052 * A193822 A202699 A058137

Adjacent sequences:  A128501 A128502 A128503 * A128505 A128506 A128507

KEYWORD

sign,easy

AUTHOR

Wolfdieter Lang Apr 04 2007

STATUS

approved

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Last modified October 22 20:54 EDT 2014. Contains 248411 sequences.