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A277168 Coefficients in the series reversion of x*exp(-x^2). 1
1, 6, 300, 41160, 11022480, 4870182240, 3211179491520, 2955402450000000, 3619848890071814400, 5693251850259515942400, 11182902317022859155532800, 26829777470359851910918195200, 77205601373291015625000000000000, 262462731609500617105685266652160000, 1040649406375513845021644881423595520000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Central terms of triangle A201685.

a(n) is the number of connected endofunctions on {1,2,...,2*n-1} that have exactly n nodes in the unique cycle of its digraph representation.

LINKS

Table of n, a(n) for n=1..15.

FORMULA

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

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

(2) A(x) = x*exp(A(x)^2).

(3) A(x) = Sum_{n>=1} (2*n-1)^(n-2) * x^(2*n-1) / (n-1)!.

(4) A(x)^2 = Sum_{n>=1} (2*n)^(n-1) * x^(2*n) / n!.

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

a(n) = binomial(2*n-1, n-1) * (2*n-1)^(n-2) * n!.

a(n) ~ 2^(3*n-5/2) * n^(2*n-2) / exp(n+1/2). - Vaclav Kotesovec, Oct 07 2016

EXAMPLE

E.g.f.: A(x) = x + 6*x^3/3! + 300*x^5/5! + 41160*x^7/7! + 11022480*x^9/9! + 4870182240*x^11/11! + 3211179491520*x^13/13! + 2955402450000000*x^15/15! +...

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

E.g.f. may also be written

A(x) = x + 3^0*x^3/1! + 5^1*x^5/2! + 7^2*x^7/3! + 9^3*x^9/4! + 11^4*x^11/5! +...

which satisfies: A(x) = x*exp(A(x)^2).

The square of the e.g.f. may be expressed as:

A(x)^2 = 2^0*x^2/1! + 4^1*x^4/2! + 6^2*x^6/3! + 8^3*x^8/4! + 10^4*x^10/5! +...

which equals LambertW(-2*x^2)/(-2).

MATHEMATICA

Table[Binomial[2*n-1, n-1]*(2*n-1)^(n-2)*n!, {n, 1, 15}] (* Vaclav Kotesovec, Oct 07 2016 *)

PROG

(PARI) {a(n) = (2*n-1)! * polcoeff( serreverse(x*exp(-x^2 +O(x^(2*n)))), 2*n-1)}

for(n=1, 20, print1(a(n), ", "))

(PARI) {a(n) = binomial(2*n-1, n-1) * (2*n-1)^(n-2) * n! }

for(n=1, 20, print1(a(n), ", "))

CROSSREFS

Cf. A201685.

Sequence in context: A264706 A066718 A065947 * A081321 A159494 A221850

Adjacent sequences:  A277165 A277166 A277167 * A277169 A277170 A277171

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Oct 01 2016

STATUS

approved

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Last modified June 19 00:55 EDT 2019. Contains 324217 sequences. (Running on oeis4.)