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A098269 a(n) = 2^n*P_n(4), 2^n times the Legendre polynomial of order n at 4. 3
1, 8, 94, 1232, 16966, 240368, 3468844, 50712992, 748553926, 11131168688, 166498969924, 2502416381792, 37759888297756, 571681667171168, 8679980422677784, 132116085646644032, 2015249400937940806 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

Central coefficients of (1+8x+15x^2)^n. 2^n*LegendreP(n,k) yields the central coefficients of (1+2kx+(k^2-1)x^2)^n, with g.f. 1/sqrt(1-4kx+4x^2).

16th binomial transform of 2^n*LegendreP(n,-4) = (-1)^n*A098269(n). - Paul Barry, Sep 03 2004

Diagonal of rational functions 1/(1 + x + 3*y + x*z - 2*x*y*z), 1/(1 - x + y + 3*x*z - 2*x*y*z), 1/(1 - x - x*y - 3*y*z - 2*x*y*z). - Gheorghe Coserea, Jul 03 2018

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

Hacène Belbachir and Abdelghani Mehdaoui, Recurrence relation associated with the sums of square binomial coefficients, Quaestiones Mathematicae (2021) Vol. 44, Issue 5, 615-624.

Hacène Belbachir, Abdelghani Mehdaoui, and László Szalay, Diagonal Sums in the Pascal Pyramid, II: Applications, J. Int. Seq., Vol. 22 (2019), Article 19.3.5.

FORMULA

G.f.: 1/sqrt(1-16x+4x^2).

a(n) = Sum_{k=0..floor(n/2)} (-1)^k*binomial(n, k)*binomial(2(n-k), n)*4^(n-2k).

E.g.f.: exp(8*x)*BesselI(0, 2*sqrt(15)*x), cf. A084770. - Vladeta Jovovic, Sep 01 2004

a(n) = Sum_{k=0..n} binomial(n,k)^2 * 3^k * 5^(n-k). - Paul D. Hanna, Sep 29 2012

D-finite with recurrence: n*a(n) = 8*(2*n-1)*a(n-1) - 4*(n-1)*a(n-2). - Vaclav Kotesovec, Oct 14 2012

a(n) ~ sqrt(450+120*sqrt(15))*(8+2*sqrt(15))^n/(30*sqrt(Pi*n)). - Vaclav Kotesovec, Oct 14 2012

MATHEMATICA

Table[SeriesCoefficient[1/Sqrt[1-16*x+4*x^2], {x, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Oct 14 2012 *)

PROG

(PARI) a(n)=pollegendre(n, 4)<<n \\ Charles R Greathouse IV, Oct 24 2011

(PARI) {a(n)=sum(k=0, n, binomial(n, k)^2*3^k*5^(n-k))} \\ Paul D. Hanna, Sep 29 2012

CROSSREFS

Cf. A069835, A084773.

Sequence in context: A299846 A214385 A121161 * A010565 A299002 A299669

Adjacent sequences:  A098266 A098267 A098268 * A098270 A098271 A098272

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Sep 01 2004

STATUS

approved

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Last modified September 28 21:22 EDT 2021. Contains 347717 sequences. (Running on oeis4.)