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Search: id:A118346
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| 1, 1, 5, 30, 201, 1445, 10900, 85128, 682505, 5585115, 46461437, 391743850, 3340361700, 28755475180, 249572076200, 2181469638880, 19186562661273, 169677521094215, 1507881643936015, 13458730170115778, 120599648894147185
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OFFSET
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0,3
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COMMENT
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Also, g.f. A(x) = (1/x)*series_reversion of x/(1 + x*GF(A005572)), where GF(A005572) is the g.f. of A005572, which is the number of walks on cubic lattice starting and finishing on the xy plane and never going below it.
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FORMULA
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G.f. A=A(x) satisfies: A = 1 - 2*x*A + 2*x*A^2 + x*A^3. G.f.: A(x) = 1 + series_reversion[x/((1+x)*(1+4*x+x^2))]. G.f.: A(x) = (1/x)*series_reversion[ x*(1-2*x+sqrt((1-2*x)*(1-6*x)))/2/(1-2*x) ].
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PROGRAM
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(PARI) {a(n)=polcoeff(serreverse(x*(1-2*x+sqrt((1-2*x)*(1-6*x)+x*O(x^n)))/2/(1-2*x))/x, n)}
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CROSSREFS
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Cf. A118345, A118347, A118348, A118349.
Sequence in context: A090139 A107265 A128328 this_sequence A091927 A082301 A144180
Adjacent sequences: A118343 A118344 A118345 this_sequence A118347 A118348 A118349
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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), Apr 26 2006
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