A128419 Expansion of 8/(sqrt(1-8*x)*(sqrt(1-8*x)+4*x+7)).

1, 4, 25, 168, 1181, 8524, 62609, 465616, 3495013, 26423604, 200920985, 1534936440, 11771854381, 90578698396, 698921030945, 5406132020128, 41905249405301, 325434733291396, 2531523208218665, 19721766268370248, 153847524455503421, 1201601094053039596, 9395224234956935345

Offset

0,2

Comments

Diagonal sums of number triangle A128417.

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..300

Formula

a(n) = Sum_{k=0..floor(n/2)} 2^(n-2k)*C(2n-2k,n-2k).

D-finite with recurrence: 3*n*(15*n-22)*a(n) = 4*(75*n^2-155*n+63)*a(n-1) + (465*n^2-922*n+336)*a(n-2) + 4*(2*n-3)*(15*n-7)*a(n-3) . - Vaclav Kotesovec, Oct 20 2012

a(n) ~ 2^(3*n+4)/(15*sqrt(Pi*n)) . - Vaclav Kotesovec, Oct 20 2012

Mathematica

CoefficientList[Series[8/(Sqrt[1-8x](Sqrt[1-8x]+4x+7)), {x, 0, 30}], x] (* Harvey P. Dale, Apr 24 2012 *)
Table[Sum[2^(n-2*k)*Binomial[2*n-2*k, n-2*k], {k, 0, Floor[n/2]}], {n, 0, 50}] (* G. C. Greubel, Feb 09 2017 *)

Prog

(PARI) x='x+O('x^50); Vec(8/(sqrt(1-8*x)*(sqrt(1-8*x)+4*x+7))) \\ G. C. Greubel, Feb 09 2017

Crossrefs

Sequence in context: A184755 A357223 A074422 * A226945 A225137 A229255

Adjacent sequences: A128416 A128417 A128418 * A128420 A128421 A128422

Keyword

easy,nonn

Author

Paul Barry, Mar 02 2007

Status

approved