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A159318 a(n) = 2^(n^2+n) * binomial(2*n-1 + 1/2^n, n) / (n*2^n + 1). 3
1, 2, 26, 1804, 591894, 860081340, 5338683113364, 138637536961147800, 14872932935424544987110, 6538678365573711555851779180, 11717380780236748297970244719026812 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

G. C. Greubel, Table of n, a(n) for n = 0..56

FORMULA

a(n) = [x^n] {(1-sqrt(1 - 2^(n+3)*x))/(2^(n+2)*x)}^(1/2^n).

G.f.: A(x) = Sum_{n>=0} a(n)*x^n/2^(n^2+n).

G.f.: A(x) = Sum_{n>=0} log(F(x/2^n))^n/n! where F(x) = (1-sqrt(1-4*x))/(2*x) is the Catalan function (A000108).

Radius of convergence of A(x) is |x| <= 1/2.

a(n) = [x^n] (1/(1 - 2^(n+1)*x)^(n + 1/2^n))/(n*2^n + 1). - Paul D. Hanna, Jun 15 2010

EXAMPLE

G.f.: A(x) = 1 + 2*x/2^2 + 26*x^2/2^6 + 1804*x^3/2^12 + 591894*x^4/2^20 + ...

G.f.: A(x) = Sum_{n>=0} log( 2^n*(1-sqrt(1 - 4*x/2^n))/(2*x) )^n/n!.

A(x) = 1 + log(F(x/2)) + log(F(x/4))^2/2! + log(F(x/8))^3/3! + ... where F(x) = (1-sqrt(1 - 4*x))/(2*x).

Special values.

A(1/2) = 1 + log(2) + log(4-4*sqrt(1/2))^2/2! + log(8-8*sqrt(3/4))^3/3! + log(16-16*sqrt(7/8))^4/4! + ...

A(1/2) = 1.70573970062357248928512380703308976974285275...

A(-1/2) = 1 + log(2*sqrt(2)-2) + log(4*sqrt(3/2)-4)^2/2! + log(8*sqrt(5/4)-8)^3/3! + log(16*sqrt(9/8)-16)^4/4! + ...

A(-1/2) = 0.81741280310249092844743171863299249334671633...

Illustrate a(n) = [x^n] {(1-sqrt(1-2^(n+3)*x))/(2^(n+2)*x)}^(1/2^n):

n=0: (1) + 2*x + 8*x^2 + 40*x^3 + 224*x^4 + 1344*x^5 + ...

n=1: 1 + (2)*x + 14*x^2 + 132*x^3 + 1430*x^4 + 16796*x^5 + ...

n=2: 1 + 2*x + (26)*x^2 + 476*x^3 + 10150*x^4 + 236060*x^5 + ...

n=3: 1 + 2*x + 50*x^2 + (1804)*x^3 + 76342*x^4 + 3534076*x^5 + ...

n=4: 1 + 2*x + 98*x^2 + 7020*x^3 + (591894)*x^4 + 54673468*x^5 + ...

n=5: 1 + 2*x + 194*x^2 + 27692*x^3 + 4660950*x^4 + (860081340)*x^5 + ...

coefficients in parenthesis form the initial terms of this sequence.

MATHEMATICA

Table[2^(n^2 +n)*Binomial[2*n -1 +1/2^n, n]/(n*2^n +1), {n, 0, 50}] (* G. C. Greubel, Jun 26 2018 *)

PROG

(PARI) a(n)=2^(n^2+n)*binomial(2*n-1+1/2^n, n)/(n*2^n + 1)

(PARI) a(n)=polcoeff(((1-sqrt(1 - 2^(n+3)*x))/2^(n+2)/x)^(1/2^n), n)

(PARI) {a(n)=polcoeff(1/(1-2^(n+1)*x+x*O(x^n))^(n+1/2^n), n)/(n*2^n+1)} \\ Paul D. Hanna, Jun 15 2010

(MAGMA) [2^(n^2 +n)*Binomial(2*n -1 +1/2^n, n)/(n*2^n +1): n in [0..50]]; // G. C. Greubel, Jun 26 2018

CROSSREFS

Cf. A159558, A159478, A158093, A000108.

Sequence in context: A209916 A337578 A156213 * A318132 A134795 A268667

Adjacent sequences:  A159315 A159316 A159317 * A159319 A159320 A159321

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Apr 22 2009

STATUS

approved

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Last modified December 2 08:31 EST 2021. Contains 349437 sequences. (Running on oeis4.)