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A143560
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G.f. satisfies: A(x) = 1 + x*A(x)/A(-x) + x^2*A(x)^2/A(-x)^2.
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0
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1, 1, 3, 6, 16, 38, 110, 276, 818, 2158, 6528, 17766, 54622, 151852, 472674, 1334886, 4195328, 11992486, 37981982, 109622228, 349384626, 1016304750, 3256170672, 9533400198, 30680043630, 90318157804, 291763419458, 862944630022
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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EXAMPLE
| A(x) = 1 + x + 3*x^2 + 6*x^3 + 16*x^4 + 38*x^5 + 110*x^6 + 276*x^7 +...
A(x)/A(-x) = 1 + 2*x + 2*x^2 + 8*x^3 + 14*x^4 + 46*x^5 + 96*x^6 +...
A(x)^2/A(-x)^2 = 1 + 4*x + 8*x^2 + 24*x^3 + 64*x^4 + 180*x^5 +...
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PROG
| (PARI) {a(n)=local(A=1+x*O(x^n)); for(i=0, n, B=A/subst(A, x, -x); A=1+x*B+x^2*B^2); polcoeff(A, n)}
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CROSSREFS
| Sequence in context: A190735 A096588 A073079 * A001675 A168317 A188442
Adjacent sequences: A143557 A143558 A143559 * A143561 A143562 A143563
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KEYWORD
| nonn
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AUTHOR
| Paul D. Hanna (pauldhanna(AT)juno.com), Aug 24 2008
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