A026955 a(n) = Sum_{k=0..n} (k+1) * T(n,k), with T given by A026386.

1, 3, 8, 25, 60, 175, 400, 1125, 2500, 6875, 15000, 40625, 87500, 234375, 500000, 1328125, 2812500, 7421875, 15625000, 41015625, 85937500, 224609375, 468750000, 1220703125, 2539062500, 6591796875, 13671875000, 35400390625

Offset

0,2

Links

Andrew Howroyd, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (0,10,0,-25).

Formula

a(n) = (n + 2) * (7 - 3*(-1)^n) * 5^floor(n/2) / 10 for n > 0.

From Colin Barker, Oct 13 2012: (Start)

a(n) = 10*a(n-2) - 25*a(n-4) for n>4.

G.f.: (5*x^4-5*x^3-2*x^2+3*x+1)/(5*x^2-1)^2. (End)

Prog

(PARI) a(n) = if(n==0, 1, (n + 2) * (7 - 3*(-1)^n) * 5^floor(n/2) / 10) \\ Andrew Howroyd, Dec 27 2024

Crossrefs

Cf. A026386.

Sequence in context: A076049 A026970 A026980 * A093900 A018789 A203413

Adjacent sequences: A026952 A026953 A026954 * A026956 A026957 A026958

Keyword

nonn,easy

Author

Clark Kimberling

Status

approved