login
This site is supported by donations to The OEIS Foundation.
Logo

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A023053 Number of noncrossing rooted trees with n nodes on a circle that do not have leaves at level 1. 1
1, 0, 2, 7, 34, 171, 905, 4952, 27802, 159254, 927081, 5468960, 32621669, 196422509, 1192294778, 7288208927, 44825586130, 277196752569, 1722454028174, 10749430579118, 67346519863117, 423425225290485 (list; graph; refs; listen; history; internal format)
OFFSET

1,3

LINKS

Index entries for sequences related to rooted trees

FORMULA

sum((-1)^i*(i+1)*binomial(3*n-2*i, n-i)/(2*n-i+1), i=0..n); G.f.: g/(1+zg) where g = 1 + z g^3, g(0) = 1 or g := 2*sin(arcsin(sqrt(27*z)/2)/3)/sqrt(3*z).

G.f.: A(x)=1/(1+x)*(1+6*x/((1+x)*G(0)-6*x)) ; G(k)= 3*x*(3*k+1)*(3*k+2) + (2*k+2)*(2*k+3) - 6*x*(k+1)*(2*k+3)*(3*k+4)*(3*k+5)/G(k+1) ; (continued fraction Euler's kind,1-step ). - Sergei N. Gladkovskii, Dec 29 2011

CROSSREFS

Sequence in context: A014623 A144005 A143889 * A058915 A020054 A206240

Adjacent sequences:  A023050 A023051 A023052 * A023054 A023055 A023056

KEYWORD

nonn

AUTHOR

Emeric Deutsch (deutsch(AT)duke.poly.edu)

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified February 17 18:34 EST 2012. Contains 206074 sequences.