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A084774
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Coefficients of 1/sqrt(1-14*x+9*x^2); also, a(n) is the central coefficient of (1+7x+10x^2)^n.
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2
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1, 7, 69, 763, 8881, 106407, 1298949, 16065483, 200630241, 2524253767, 31947470149, 406281388443, 5187375332881, 66454791792487, 853788052488069, 10996378059281643, 141934540736139201, 1835494145265388167
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OFFSET
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0,2
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COMMENTS
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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.
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REFERENCES
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P. Barry, On the Central Coefficients of Riordan Matrices, Journal of Integer Sequences, 16 (2013), #13.5.1.
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LINKS
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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
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FORMULA
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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
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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Cf. A006442.
Sequence in context: A219330 A122010 A180911 * A025757 A243668 A226270
Adjacent sequences: A084771 A084772 A084773 * A084775 A084776 A084777
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna, Jun 11 2003
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STATUS
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approved
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