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A367666
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G.f. A(x) satisfies A(x) = 1 / (1 - x - x^2 * A(x^3)).
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2
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1, 1, 2, 3, 5, 9, 15, 26, 46, 79, 138, 241, 418, 729, 1270, 2209, 3849, 6703, 11669, 20325, 35393, 61629, 107329, 186900, 325464, 566779, 986987, 1718745, 2993062, 5212135, 9076470, 15805899, 27524544, 47931568, 83468632, 145353195, 253119779, 440785795
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OFFSET
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0,3
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LINKS
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FORMULA
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a(0) = 1; a(n) = a(n-1) + Sum_{k=0..floor((n-2)/3)} a(k) * a(n-2-3*k).
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MAPLE
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option remember;
if n = 0 then
1;
else
procname(n-1) + add(procname(k) * procname(n-2-3*k), k=0..floor((n-2)/3)) ;
end if;
end proc:
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PROG
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(PARI) a_vector(n) = my(v=vector(n+1)); v[1]=1; for(i=1, n, v[i+1]=v[i]+sum(j=0, (i-2)\3, v[j+1]*v[i-1-3*j])); v;
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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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