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A098460
Expansion of e.g.f. 1/sqrt(1-2x-2x^2).
1
1, 1, 5, 33, 321, 3945, 59445, 1056825, 21677985, 503799345, 13084021125, 375524312625, 11803392302625, 403235809601625, 14876913457531125, 589498927632239625, 24969077812488434625, 1125803018759825030625
OFFSET
0,3
FORMULA
a(n) = (n!/2^n)*A084609(n);
a(n) = (n!/2^n) * Sum_{k=0..floor(n/2)} binomial(n,k)*binomial(2(n-k),n)*2^k;
a(n) = n! * Sum_{k=0..floor(n/2)} binomial(n,k)*binomial(2(n-k),n)*2^(k-n).
D-finite with recurrence: a(n) +(1-2*n)*a(n-1) -2*(n-1)^2*a(n-2)=0. - R. J. Mathar, Nov 15 2011
a(n) ~ 2^(n+1/2)*n^n/(sqrt(3-sqrt(3))*exp(n)*(sqrt(3)-1)^n). - Vaclav Kotesovec, Jun 26 2013
MATHEMATICA
CoefficientList[Series[1/Sqrt[1-2*x-2*x^2], {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Jun 26 2013 *)
PROG
(PARI) my(x='x+O('x^25)); Vec(serlaplace(1/sqrt(1-2*x-2*x^2))) \\ Michel Marcus, May 10 2020
CROSSREFS
Cf. A012244.
Sequence in context: A001828 A084845 A198079 * A087618 A322178 A134152
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Sep 08 2004
STATUS
approved