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A168554
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G.f.: A(x) = Sum_{n>=0} 2^(n^2)*A000108(n)*(1-2^n*x)^n*x^n where A000108 is the Catalan numbers.
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1
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1, 2, 28, 2304, 856576, 1351057408, 8846893121536, 238036693238677504, 26163011929227894194176, 11701653843176682031379644416, 21237338088859808279441141143699456
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OFFSET
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0,2
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COMMENTS
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Compare the g.f. to: Sum_{n>=0} A000108(n)*(1-x)^n*x^n = 1/(1-x).
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LINKS
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FORMULA
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a(n) = [x^n] 2/(1 + sqrt(1 - 4*2^n*(x-x^2))).
a(n) = Sum_{k=0..[n/2]} (-1)^k*2^(n(n-k))*C(n-k,k)*A000108(n-k).
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EXAMPLE
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G.f.: A(x) = 1 + 2*x + 28*x^2 + 2304*x^3 + 856576*x^4 +...
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MAPLE
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S:= add(2^(n^2)*binomial(2*n, n)/(n+1)*(1-2^n*x)^n*x^n, n=0..30):
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MATHEMATICA
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Table[Sum[(-1)^k*2^(n(n-k))*Binomial[n-k, k]*Binomial[2*(n-k), (n-k)]/(n-k+1), {k, 0, Floor[n/2]}], {n, 0, 20}] (* G. C. Greubel, Nov 13 2016 *)
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PROG
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(PARI) {a(n)=polcoeff(sum(m=0, n, 2^(m^2)*binomial(2*m, m)/(m+1)*x^m*(1-2^m*x)^m)+x*O(x^n), n)}
(PARI) {a(n)=polcoeff(2/(1+sqrt(1-4*2^n*(x-x^2) +x*O(x^n))), n)}
(PARI) {a(n)=sum(k=0, n\2, (-1)^k*2^(n*(n-k))*binomial(n-k, k)*binomial(2*n-2*k, n-k)/(n-k+1))}
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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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