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A152282
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Coefficients in a q-analog of the LambertW function at q=2: A(x) = Sum_{n>=0} a(n)*x^n/faq(n,2) where faq(n,q) = q-factorial of n.
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2
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1, 1, 4, 43, 1076, 58746, 6772360, 1619251271, 794625904404, 795206398610710, 1615965837952912216, 6649024230536100958062, 55277445682961080929146824, 927088288759058912165347148404, 31329256772332779793923906186541200
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OFFSET
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0,3
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LINKS
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FORMULA
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G.f. satisfies: A(x) = e_q( x*A(x), 2) and A( x/e_q(x,2) ) = e_q(x,2) where e_q(x,q) = Sum_{n>=0} x^n/faq(n,q) is the q-exponential function.
G.f.: A(x) = (1/x)*Series_Reversion( x/e_q(x,2) ).
G.f. satisfies: A(x) = exp( Sum_{n>=1} -A(x)^n*(-x)^n/(n*(2^n-1)) ). [Paul D. Hanna, Oct 24 2011]
a(n) = Sum_{k=0..n(n-1)/2} A152290(n,k)*2^k.
a(n) = faq(n,2)*Sum_{pi} n!/((n-k+1)!*Product_{i=1..n} (e(i)!*faq(i,2)^e(i))), where pi runs through all nonnegative integer solutions of e(1)+2*e(2)+...+n*e(n)=n and k=e(1)+e(2)+...+e(n). [Vladeta Jovovic, Dec 03 2008]
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EXAMPLE
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G.f.: A(x) = 1 + x + 4/3*x^2 + 43/21*x^3 + 1076/315*x^4 + 58746/9765*x^5 +...
G.f. satisfies: A(x) = e_q( x*A(x), 2) where the q-exponential series is:
e_q(x,q) = 1 + x + x^2/faq(2,q) + x^3/faq(3,q) +...+ x^n/faq(n,q) +...
The q-factorial of n is faq(n,q) = Product_{k=1..n} (q^k-1)/(q-1):
faq(0,q)=1, faq(1,q)=1, faq(2,q)=(1+q), faq(3,q)=(1+q)*(1+q+q^2), faq(4,q)=(1+q)*(1+q+q^2)*(1+q+q^2+q^3), ...
Also, the logarithm of the g.f. begins:
log(A(x)) = A(x)*x/(2-1) - A(x)^2*x^2/(2*(2^2-1)) + A(x)^3*x^3/(3*(2^3-1)) - A(x)^4*x^4/(4*(2^4-1)) + A(x)^5*x^5/(5*(2^5-1)) +...
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PROG
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(PARI) {a(n, q=2)=local(e_q=1+sum(j=1, n, x^j/prod(i=1, j, (q^i-1)/(q-1))), LW_q=serreverse(x/e_q+x^2*O(x^n))/x); polcoeff(LW_q+x*O(x^n), n, x)*prod(i=1, n, (q^i-1)/(q-1))}
(PARI) {a(n)=local(A=1+x); for(i=1, n, A=exp(sum(m=1, n, -(A+x*O(x^n))^m*(-x)^m/(m*(2^m-1))))); prod(k=1, n, 2^k-1)*polcoeff(A, n)}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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