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Search: id:A120589
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| 1, 2, 3, 6, 15, 42, 126, 396, 1287, 4290, 14586, 50388, 176358, 624036, 2228700, 8023320, 29084535, 106073010, 388934370, 1432916100, 5301789570, 19692361260, 73398801060, 274447690920, 1029178840950, 3869712441972, 14585839204356
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OFFSET
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0,2
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FORMULA
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a(n) = 3*A000108(n-1) for n>=2, where A000108 is the Catalan numbers.
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EXAMPLE
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A(x) = 1 + 2*x + 3*x^2 + 6*x^3 + 15*x^4 + 42*x^5 + 126*x^6 + 396*x^7 +...
A(x)^(1/2) = 1 + x + x^2 + 2*x^3 + 5*x^4 + 14*x^5 + 42*x^6 + 132*x^7 +...
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PROGRAM
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(PARI) {a(n)=local(A=1+x+x^2+x*O(x^n)); for(i=0, n, A=A-3*A+2+x+A^2); polcoeff(A^2, n)}
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CROSSREFS
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Cf. A120588 (A(x)^(1/2)); A120590 - A120607.
Sequence in context: A129960 A115098 A036418 this_sequence A110181 A141351 A088793
Adjacent sequences: A120586 A120587 A120588 this_sequence A120590 A120591 A120592
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KEYWORD
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nonn
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AUTHOR
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Paul D. Hanna (pauldhanna(AT)juno.com), Jun 16 2006
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