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A295762
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G.f. A(x) satisfies: A(x - 2*A(x^2)) = x + A(x^2).
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2
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1, 3, 12, 69, 444, 3060, 22104, 165195, 1266636, 9908196, 78760920, 634379124, 5166150000, 42465716328, 351876854448, 2936058188877, 24648274487556, 208040487845076, 1764376309044792, 15027939263874132, 128495423551583664, 1102547377746843624, 9490542912076091184, 81931260285359287812, 709199467337528862768, 6153967855892699398368, 53521531522907694320928, 466461452477641527148344
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OFFSET
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1,2
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COMMENTS
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Odd terms seem to occur only at a(2^n) for n>=0 (conjecture).
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LINKS
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FORMULA
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G.f. A(x) satisfies:
(1) A(x) = x + 3 * A( (x + 2*A(x))^2/9 ).
(2) A(x) = -x/2 + 3/2*Series_Reversion( x - 2*A(x^2) ).
(3) x = A( -2*x + 3 * Series_Reversion( x + A(x^2) ) ).
(4) A(x - 2*A(x^2)) = x + A(x^2).
a(n) ~ c * d^n / n^(3/2), where d = 9.2093789571628170578048631587867514135871993630966974111785256401203919511... and c = 0.0682994378249920600052979267397719638823914060552824374... - Vaclav Kotesovec, Dec 04 2017
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EXAMPLE
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G.f.: A(x) = x + 3*x^2 + 12*x^3 + 69*x^4 + 444*x^5 + 3060*x^6 + 22104*x^7 + 165195*x^8 + 1266636*x^9 + 9908196*x^10 + 78760920*x^11 + 634379124*x^12 +...
such that A(x - 2*A(x^2)) = x + A(x^2).
RELATED SERIES.
A(x - 2*A(x^2)) = x + x^2 + 3*x^4 + 12*x^6 + 69*x^8 + 444*x^10 + 3060*x^12 + 22104*x^14 + 165195*x^16 + 1266636*x^18 + 9908196*x^20 +...
which equals x + A(x^2).
Series_Reversion( x - 2*A(x^2) ) = x + 2*x^2 + 8*x^3 + 46*x^4 + 296*x^5 + 2040*x^6 + 14736*x^7 + 110130*x^8 + 844424*x^9 + 6605464*x^10 + 52507280*x^11 + 422919416*x^12 +...
which equals (2*A(x) + x)/3.
A( (x + 2*A(x))^2/9 ) = x^2 + 4*x^3 + 23*x^4 + 148*x^5 + 1020*x^6 + 7368*x^7 + 55065*x^8 + 422212*x^9 + 3302732*x^10 + 26253640*x^11 + 211459708*x^12 +...
which equals (A(x) - x)/3.
Odd terms seem to occur only at positions 2^n, n>=0, beginning:
[1, 3, 69, 165195, 2936058188877, 2740954751925406954539018771, 6899036855844990995854505818787102393537422152828959745477, ...].
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MATHEMATICA
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nmax = 28; sol = {a[1] -> 1}; Do[A[x_] = Sum[a[k] x^k, {k, 1, n}] /. sol; eq = CoefficientList[A[x - 2 A[x^2]] - (x + A[x^2]) + O[x]^(n+1) // Normal, x] == 0 /. sol; sol = sol ~Join~ Solve[eq][[1]], {n, 1, nmax}];
sol /. Rule -> Set;
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PROG
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(PARI) {a(n) = my(A=x); for(i=1, n, A = -x/2 + 3/2*serreverse(x - 2*subst(A, x, x^2) +x^2*O(x^n)) ); polcoeff(A, 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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