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A168406
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E.g.f.: Sum_{n>=0} arctan(2^n*x)^n/n!.
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2
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1, 2, 16, 496, 63488, 32899840, 68049141760, 560546415810560, 18415229458563727360, 2416302337337071616327680, 1267360474688679165942982246400, 2658246833688954938616062542151680000
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = [x^n/n!] exp(2^n*arctan(x)) for n >= 0.
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EXAMPLE
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E.g.f.: A(x) = 1 + 2*x + 16*x^2/2! + 496*x^3/3! + 63488*x^4/4! + ...
A(x) = 1 + arctan(2*x) + arctan(4*x)^2/2! + arctan(8*x)^3/3! + arctan(16*x)^4/4! + ... + arctan(2^n*x)^n/n! + ...
a(n) = coefficient of x^n/n! in G(x)^(2^n) where G(x) = exp(arctan(x)):
G(x) = 1 + x + x^2/2! - x^3/3! - 7*x^4/4! + 5*x^5/5! + 145*x^6/6! + ... + A002019(n)*x^n/n! + ...
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PROG
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(PARI) {a(n)=n!*polcoeff(sum(k=0, n, atan(2^k*x +x*O(x^n))^k/k!), n)}
(PARI) {a(n)=n!*polcoeff(exp(2^n*atan(x +x*O(x^n))), 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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