login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A242087 Number of balanced orbitals over an odd number of sectors. 3
1, 0, 6, 6, 36, 88, 376, 1096, 4476, 14200, 57284, 190206, 764812, 2615268, 10499504, 36677626, 147110276, 522288944 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

See A241810 and A232500 for the combinatorial definitions.

LINKS

Table of n, a(n) for n=0..17.

FORMULA

a(n) = A241810(2*n+1).

MATHEMATICA

np[z_]:=Module[{i, j}, For[i=Length[z], i>1&&z[[i-1]]>=z[[i]], i--]; For[j=Length[z], z[[j]]<=z[[i-1]], j--]; Join[Take[z, i-2], {z[[j]]}, Reverse[Drop[ReplacePart[z, z[[i-1]], j], i-1]]]]; o=Table[1, {16}];

Print[1]; Do[p=Join[-Take[o, n], {0}, Take[o, n]]; c=0; Do[If[Accumulate[Accumulate[p]][[-1]]==0, c++]; p=np[p], {(2*n+1)!/(2*n!^2)}]; Print[2*c], {n, 16}]

(* Hans Havermann, May 10 2014 *)

PROG

(Sage)

def A242087(n):

    if n == 0: return 1

    A = 0; T = [0]

    for i in (1..n):

        T.append(-1); T.append(1)

    for p in Permutations(T):

        P = 0; S = 0

        for k in (0..2*n):

            P += p[k]; S += P

        if S == 0: A += 1

    return A

[A242087(n) for n in (0..10)]

CROSSREFS

Sequence in context: A176861 A245131 A038260 * A217978 A257626 A222340

Adjacent sequences:  A242084 A242085 A242086 * A242088 A242089 A242090

KEYWORD

nonn,more

AUTHOR

Peter Luschny, May 04 2014

EXTENSIONS

More terms from Hans Havermann, May 10 2014

a(17) from Hans Havermann, May 23 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified June 1 02:09 EDT 2020. Contains 334758 sequences. (Running on oeis4.)