A073782 a(n) = Sum_{k=0..n} S(k)*S(n-k), convolution of S=A001644 with itself.

9, 6, 19, 48, 89, 190, 391, 784, 1577, 3142, 6219, 12256, 24041, 46974, 91471, 177568, 343753, 663814, 1278979, 2459152, 4719417, 9041470, 17294039, 33030320, 62999145, 120006214, 228327099, 433939904, 823854793, 1562602238

Offset: 0

Author

Mario Catalani (mario.catalani(AT)unito.it), Aug 11 2002

Keywords

• easy
• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 0..1000
• Index entries for linear recurrences with constant coefficients, signature (2,1,0,-3,-2,-1).

Crossrefs

Cf. A001644.

Programs

Magma

R:=PowerSeriesRing(Integers(), 30); Coefficients(R!( (3-2*x-x^2)^2/(1-x-x^2-x^3)^2 )); // G. C. Greubel, Apr 12 2019

Mathematica

CoefficientList[Series[(3-2x-x^2)^2/(1-x-x^2-x^3)^2, {x, 0, 30}], x]

PARI

my(x='x+O('x^30)); Vec((3-2*x-x^2)^2/(1-x-x^2-x^3)^2) \\ G. C. Greubel, Apr 12 2019

Sage

((3-2*x-x^2)^2/(1-x-x^2-x^3)^2).series(x, 30).coefficients(x, sparse=False) # G. C. Greubel, Apr 12 2019

Formula

G.f.: (3-2*x-x^2)^2/(1-x-x^2-x^3)^2.