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A273952 E.g.f. A(x) satisfies: A( sqrt( A(x^2*exp(-x)) ) ) = x, where A(x) = Sum_{n>=1} a(n)*x^n/(2^(n-1)*(n-1)!). 1
1, 1, 1, 4, 77, 736, 2077, 22912, 1197625, 23597056, 350173241, 7161708544, 236337969925, 6751323455488, 122041278706453, 3799979465506816, 298712815532930033, 10872130692620222464, -18153139467375673487, -513247768690867306496, 1172597577739561586096701, 53608628175847428085252096, -748272864671493582192607219, -39715579516869644288006291456, 7586072261976188853665242247977 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

LINKS

Table of n, a(n) for n=1..25.

FORMULA

E.g.f. A(x) = Sum_{n>=1} a(n) * x^n / (2^(n-1)*(n-1)!) satisfies:

(1) A( sqrt( A(x^2*exp(x)) ) ) = -2*LambertW(-x/2*exp(x/2)).

(2) A(x) = Series_Reversion( sqrt( A(x^2*exp(-x)) ) ).

EXAMPLE

E.g.f. A(x) = x + x^2/2 + x^3/(2^2*2!) + 4*x^4/(2^3*3!) + 77*x^5/(2^4*4!) + 736*x^6/(2^5*5!) + 2077*x^7/(2^6*6!) + 22912*x^8/(2^7*7!) + 1197625*x^9/(2^8*8!) + 23597056*x^10/(2^9*9!) + 350173241*x^11/(2^10*10!) + 7161708544*x^12/(2^11*11!) + 236337969925*x^13/(2^12*12!) + 6751323455488*x^14/(2^13*13!) + 122041278706453*x^15/(2^14*14!) +...

such that: A( sqrt( A(x^2*exp(-x)) ) ) = x.

Written with reduced fraction coefficients,

A(x) = x + 1/2*x^2 + 1/8*x^3 + 1/12*x^4 + 77/384*x^5 + 23/120*x^6 + 2077/46080*x^7 + 179/5040*x^8 + 239525/2064384*x^9 + 823/6480*x^10 + 350173241/3715891200*x^11 + 109279/1247400*x^12 + 9453518797/78479622144*x^13 + 206034041/1556755200*x^14 + 122041278706453/1428329123020800*x^15 +...

Also, A( sqrt( A(x^2*exp(x)) ) ) = -2*LambertW(-x/2*exp(x/2)) where

A( sqrt( A(x^2*exp(x)) ) ) = x + 2*x^2/2! + 6*x^3/3! + 28*x^4/4! + 180*x^5/5! + 1476*x^6/6! +...+ A100526(n)*x^n/n! +...

PROG

(PARI) {a(n) = my(A=x); for(i=1, n, A = serreverse( sqrt( subst(A, x, x^2*exp(-x +x*O(x^n))) ) ) ); (n-1)!*2^(n-1) * polcoeff(A, n)}

for(n=1, 30, print1(a(n), ", "))

CROSSREFS

Cf. A100526.

Sequence in context: A184272 A080989 A006267 * A201984 A210519 A279437

Adjacent sequences:  A273949 A273950 A273951 * A273953 A273954 A273955

KEYWORD

sign

AUTHOR

Paul D. Hanna, Jun 16 2016

STATUS

approved

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Last modified April 24 22:26 EDT 2019. Contains 322446 sequences. (Running on oeis4.)