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A084774 Coefficients of 1/sqrt(1-14*x+9*x^2); also, a(n) is the central coefficient of (1+7x+10x^2)^n. 2
1, 7, 69, 763, 8881, 106407, 1298949, 16065483, 200630241, 2524253767, 31947470149, 406281388443, 5187375332881, 66454791792487, 853788052488069, 10996378059281643, 141934540736139201, 1835494145265388167 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

G.f.: 1/sqrt(1-2*b*x+(b^2-4*c)*x^2) yields central coefficients of (1+b*x+c*x^2)^n.

REFERENCES

P. Barry, On the Central Coefficients of Riordan Matrices, Journal of Integer Sequences, 16 (2013), #13.5.1.

LINKS

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

V. Kotesovec, Asymptotic of a sums of powers of binomial coefficients * x^k, 2012

FORMULA

a(n) = Sum_{k=0..n} binomial(n,k)^2 * 2^k * 5^(n-k). - Paul D. Hanna, Sep 28 2012

Recurrence: n*a(n) = 7*(2*n-1)*a(n-1) - 9*(n-1)*a(n-2). - Vaclav Kotesovec, Oct 14 2012

a(n) ~ sqrt(200+70*sqrt(10))*(7+2*sqrt(10))^n/(20*sqrt(Pi*n)) = (sqrt(2)+sqrt(5))^(2*n+1)/(2*10^(1/4)*sqrt(Pi*n)). - Vaclav Kotesovec, Oct 14 2012

MATHEMATICA

Table[Sum[Binomial[n, k]^2*2^k*5^(n-k), {k, 0, n}], {n, 0, 20}] (* Vaclav Kotesovec, Oct 14 2012 *)

Table[n! SeriesCoefficient[E^(7 x) BesselI[0, 2 Sqrt[10] x], {x, 0, n}], {n, 0, 20}] (* Vincenzo Librandi, May 10 2013 *)

PROG

(PARI) for(n=0, 30, t=polcoeff((1+7*x+10*x^2)^n, n, x); print1(t", "))

(PARI) {a(n)=sum(k=0, n, binomial(n, k)^2*2^k*5^(n-k))} - Paul D. Hanna, Sep 28 2012

CROSSREFS

Cf. A006442.

Sequence in context: A219330 A122010 A180911 * A025757 A243668 A226270

Adjacent sequences:  A084771 A084772 A084773 * A084775 A084776 A084777

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Jun 11 2003

STATUS

approved

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Last modified November 28 23:59 EST 2014. Contains 250478 sequences.