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A272821 G.f. A(x) satisfies: A( x*A(x) - 2*x*A(x)^2 + x*A(x)^3 ) = x^2. 2
1, 2, 5, 22, 104, 508, 2581, 13590, 73255, 402096, 2240803, 12645756, 72120577, 415017628, 2406756231, 14051487550, 82524268241, 487209739242, 2889872479365, 17213187356000, 102916691619082, 617446202168776, 3715938753908449, 22427371853933596, 135714772335246022, 823237636321437554, 5004875492077075585, 30490222425814170940 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Paul D. Hanna, Table of n, a(n) for n = 1..300

EXAMPLE

G.f.: A(x) = x + 2*x^2 + 5*x^3 + 22*x^4 + 104*x^5 + 508*x^6 + 2581*x^7 + 13590*x^8 + 73255*x^9 + 402096*x^10 + 2240803*x^11 + 12645756*x^12 +...

where A( x*A(x)*(1 - A(x))^2 ) = x^2.

RELATED SERIES.

A(x)^2 = x^2 + 4*x^3 + 14*x^4 + 64*x^5 + 321*x^6 + 1652*x^7 + 8718*x^8 + 47160*x^9 + 259848*x^10 + 1452340*x^11 + 8215412*x^12 +...

A(x)^3 = x^3 + 6*x^4 + 27*x^5 + 134*x^6 + 711*x^7 + 3846*x^8 + 21104*x^9 + 117600*x^10 + 663747*x^11 + 3785068*x^12 + 21775758*x^13 +...

A(x)^4 = x^4 + 8*x^5 + 44*x^6 + 240*x^7 + 1350*x^8 + 7664*x^9 + 43736*x^10 + 251408*x^11 + 1455577*x^12 + 8480432*x^13 + 49687828*x^14 +...

A(x) - 2*A(x)^2 + A(x)^4 = x - 2*x^3 + 3*x^5 - 12*x^7 + 39*x^9 - 130*x^11 + 495*x^13 - 1932*x^15 + 7818*x^17 +...

Let B(x) be the series reversion of g.f. A(x), so that A(B(x)) = x, then

B(x) = x - 2*x^2 + 3*x^3 - 12*x^4 + 39*x^5 - 130*x^6 + 495*x^7 - 1932*x^8 + 7818*x^9 - 32496*x^10 + 137158*x^11 - 587476*x^12 + 2544253*x^13 - 11117046*x^14 + 48960141*x^15 +...

where B(x^2) = x*A(x)*(1 - A(x))^2,

also, B(B(x)^2) = x*(1-x)^2 * B(x).

The square-root of x*A(x) is an integer series:

sqrt( x*A(x) ) = x + x^2 + 2*x^3 + 9*x^4 + 41*x^5 + 195*x^6 + 973*x^7 + 5063*x^8 + 27023*x^9 + 147147*x^10 + 814736*x^11 + 4573323*x^12 + 25964578*x^13 + 148836155*x^14 + 860244693*x^15 +...+ A292078(n)*x^n +...

Given g.f. A(x), the g.f. of A292078 equals G(x) such that

(1) G(x)^2 = A(x^2),

(2) G( x*G(x) - x*G(x)^3 ) = x^2.

PROG

(PARI) {a(n) = my(A=[1, 2]); for(i=1, n, A=concat(A, 0); F=x*Ser(A); A[#A] = -Vec( subst(F, x, x*F*(1-F)^2 ) )[#A] ); A[n]}

for(n=1, 40, print1(a(n), ", "))

CROSSREFS

Cf. A292078.

Sequence in context: A056840 A321608 A241345 * A278439 A126797 A101206

Adjacent sequences:  A272818 A272819 A272820 * A272822 A272823 A272824

KEYWORD

nonn

AUTHOR

Paul D. Hanna, May 09 2016

STATUS

approved

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Last modified September 19 07:24 EDT 2020. Contains 337178 sequences. (Running on oeis4.)