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A291189
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G.f. satisfies: A(x - A(x) + A(x)^2) = -x^4.
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2
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1, 1, 2, 6, 16, 48, 152, 501, 1690, 5822, 20388, 72360, 259688, 940792, 3435904, 12636554, 46760376, 173971252, 650380288, 2441905192, 9203979808, 34813551616, 132101846848, 502732914346, 1918353118348, 7338208929260, 28134551443480, 108094972590872, 416122805092224, 1604832481200352, 6199797669769760, 23989294121910790, 92962226232374892, 360749306397285812
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OFFSET
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1,3
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COMMENTS
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At what positions n is a(n) odd?
Compare g.f. to: C(x - C(x) + C(x)^2) = 0, trivial when C(x) = x + C(x)^2 is the g.f. of the Catalan numbers (A000108).
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LINKS
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FORMULA
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G.f. A(x) satisfies: x - A(x) + A(x)^2 = Ai(-x^4) where Ai( A(x) ) = x.
a(n) ~ c * d^n / n^(3/2), where d = 4.05999022767846206402248334679744980701174... and c = 0.14415462031792796731396571657... - Vaclav Kotesovec, Aug 28 2017
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EXAMPLE
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G.f.: A(x) = x + x^2 + 2*x^3 + 6*x^4 + 16*x^5 + 48*x^6 + 152*x^7 + 501*x^8 + 1690*x^9 + 5822*x^10 + 20388*x^11 + 72360*x^12 + 259688*x^13 + 940792*x^14 + 3435904*x^15 + 12636554*x^16 + 46760376*x^17 + 173971252*x^18 + 650380288*x^19 + 2441905192*x^20 + 9203979808*x^21 +...
where A(x - A(x) + A(x)^2) = -x^4.
RELATED SERIES.
Define Ai(x) such that Ai(A(x)) = x, where Ai(x) begins:
Ai(x) = x - x^2 - x^4 + 4*x^5 - 6*x^6 + 8*x^7 - 30*x^8 + 92*x^9 - 190*x^10 + 428*x^11 - 1276*x^12 + 3524*x^13 - 8572*x^14 + 22120*x^15 - 62215*x^16 + 169464*x^17 - 444860*x^18 + 1202364*x^19 - 3340582*x^20 + 9167812*x^21 - 24936852*x^22 + 68746520*x^23 - 191319986*x^24 + 530404940*x^25 +...
then x - A(x) + A(x)^2 = Ai(-x^4),
and Ai(x) - Ai( -Ai(x)^4 ) = x - x^2.
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PROG
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(PARI) {a(n) = my(A=x, V=[1, 1, 2, 6]); for(i=1, n, V=concat(V, 0); A=x*Ser(V); V[#V]=Vec(subst(A, x, x - A + A^2))[#V-3]); V[n]}
for(n=1, 30, print1(a(n), ", "))
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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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