A094155 -id:A094155 - cp's OEIS frontend

A000939 Number of inequivalent n-gons.

1, 1, 1, 2, 4, 14, 54, 332, 2246, 18264, 164950, 1664354, 18423144, 222406776, 2905943328, 40865005494, 615376173184, 9880209206458, 168483518571798, 3041127561315224, 57926238289970076, 1161157777643184900, 24434798429947993054, 538583682082245127336

Offset: 1

N. J. A. Sloane

Here two n-gons are said to be equivalent if they differ in starting point, orientation, or by a rotation (but not by a reflection - for that see A000940).

Number of cycle necklaces on n vertices, defined as equivalence classes of (labeled, undirected) Hamiltonian cycles under rotation of the vertices. The path version is A275527. - Gus Wiseman, Mar 02 2019

			Possibilities for n-gons without distinguished vertex can be encoded as permutation classes of vertices, two permutations being equivalent if they can be obtained from each other by circular rotation, translation mod n or complement to n+1.
n=3: 123.
n=4: 1234, 1243.
n=5: 12345, 12354, 12453, 13524.
n=6: 123456, 123465, 123564, 123645, 123654, 124365, 124635, 124653, 125364, 125463, 125634, 126435, 126453, 135264.

N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence).
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Georg Fischer, Table of n, a(n) for n = 1..450 (first 100 terms by T. D. Noe)
S. W. Golomb and L. R. Welch, On the enumeration of polygons, Amer. Math. Monthly, 67 (1960), 349-353.
S. W. Golomb and L. R. Welch, On the enumeration of polygons, Amer. Math. Monthly, 67 (1960), 349-353. [Annotated scanned copy]
Samuel Herman and Eirini Poimenidou, Orbits of Hamiltonian Paths and Cycles in Complete Graphs, arXiv:1905.04785 [math.CO], 2019.
A. Stoimenow, Enumeration of chord diagrams and an upper bound for Vassiliev invariants, J. Knot Theory Ramifications, 7 (1998), no. 1, 93-114.
Eric Weisstein's World of Mathematics, Hamiltonian Cycle.
Wikipedia, Hamiltonian path.
Wikipedia, Polygon.
Gus Wiseman, Inequivalent representatives of the a(6) = 14 cycle necklaces.
Gus Wiseman, Inequivalent representatives of the a(7) = 54 n-gons.

Cf. A000940. Bisections give A094154, A094155.
For star polygons see A231091.
Cf. A000031, A002619, A002866, A006125, A008965, A059966, A060223, A192332, A275527, A323858, A323870, A324461.

with(numtheory):
# for n odd:
Ed:= proc(n) local t1, d; t1:=0; for d from 1 to n do
       if n mod d = 0 then t1:= t1+phi(n/d)^2*d!*(n/d)^d fi od:
       t1/(2*n^2)
     end:
# for n even:
Ee:= proc(n) local t1, d; t1:= 2^(n/2)*(n/2)*(n/2)!; for d
       from 1 to n do if n mod d = 0 then t1:= t1+
       phi(n/d)^2*d!*(n/d)^d; fi od: t1/(2*n^2)
     end:
A000939:= n-> if n mod 2 = 0 then ceil(Ee(n)) else ceil(Ed(n)); fi:
seq(A000939(n), n=1..25);

a[n_] := (t = If[OddQ[n], 0, 2^(n/2)*(n/2)*(n/2)!]; Do[If[Mod[n, d]==0, t = t+EulerPhi[n/d]^2*d!*(n/d)^d], {d, 1, n}]; t/(2*n^2)); a[1] := 1; a[2] := 1; Print[a /@ Range[1, 450]] (* Jean-François Alcover, May 19 2011, after Maple prog. *)
rotgra[g_,m_]:=Sort[Sort/@(g/.k_Integer:>If[k==m,1,k+1])];
Table[Length[Select[Union[Sort[Sort/@Partition[#,2,1,1]]&/@Permutations[Range[n]]],#==First[Sort[Table[Nest[rotgra[#,n]&,#,j],{j,n}]]]&]],{n,8}] (* Gus Wiseman, Mar 02 2019 *)

a(n)={if(n<3, n>=0, (if(n%2, 0, (n/2-1)!*2^(n/2-2)) + sumdiv(n, d, eulerphi(n/d)^2 * d! * (n/d)^d)/n^2)/2)} \\ Andrew Howroyd, Aug 17 2019

For formula see Maple lines.
a(2*n + 1) =  A002619(2*n + 1)/2 for n > 0; a(2*n) = (A002619(2*n) + A002866(n-1))/2 for n > 1. - Andrew Howroyd, Aug 17 2019
a(n) ~ sqrt(2*Pi)/2 * n^(n-3/2) / e^n. - Ludovic Schwob, Nov 03 2022

More terms from Pab Ter (pabrlos(AT)yahoo.com), May 05 2004

Added a(1) = 1 and a(2) = 1 by Gus Wiseman, Mar 02 2019

A094154 Bisection of A000939.

Original entry on oeis.org

1, 4, 54, 2246, 164950, 18423144, 2905943328, 615376173184, 168483518571798, 57926238289970076, 24434798429947993054, 12408968034664788792008, 7468360391233437715595634, 5256695596753687250025931048, 4278271932454694494134007741950, 3986830862631720154048770746485900

Offset: 1

N. J. A. Sloane, May 05 2004

nonn

S. W. Golomb and L. R. Welch, On the enumeration of polygons, Amer. Math. Monthly, 67 (1960), 349-353.

Cf. A000939, A094155.

with(numtheory); f:=proc(n) local t1,d; t1:=0; for d from 1 to n do if n mod d = 0 then t1:=t1+phi(n/d)^2*d!*(n/d)^d; fi; od: t1/(2*n^2); end;

See Maple line.

A358328 Triangle read by rows: T(n,k) is the number of polygons with 2n sides, of which k run through the center of a circle, on the circumference of which the 2n vertices of the polygon are arranged at equal spacing, up to rotation.

Original entry on oeis.org

0, 0, 1, 1, 0, 1, 4, 4, 4, 2, 98, 120, 84, 24, 6, 5648, 6912, 4032, 1344, 288, 40, 532344, 631680, 351360, 118408, 26400, 3840, 322, 72724122, 84211200, 45907200, 15436800, 3513600, 552960, 57600, 3294, 13577195574, 15432560640, 8305920000, 2786273280, 643507200, 106122240, 12418560, 967680, 40320

Offset: 0

Ludovic Schwob, Nov 09 2022

By "2*n-sided polygons" we mean the polygons that can be drawn by connecting 2*n equally spaced points on a circle.
T(0,0)=0 and T(0,1)=1 by convention.
The sequence is limited to even-sided polygons, since all odd-sided polygons have no side passing through the center.

			Triangle begins:
    0;
    0,   1;
    1,   0,   1;
    4,   4,   4,   2;
   98, 120,  84,  24,   6;

Ludovic Schwob, Table of n, a(n) for n = 0..5150

Row sums give A094155(n).

Cf. A330662.

cp's OEIS Frontend

A000939 Number of inequivalent n-gons.

Views

Author

Keywords

Comments

Examples

References

Links

Crossrefs

Programs

Maple

Mathematica

PARI

Formula

Extensions

A094154 Bisection of A000939.

Views

Author

Keywords

Links

Crossrefs

Programs

Maple

Formula

A358328 Triangle read by rows: T(n,k) is the number of polygons with 2n sides, of which k run through the center of a circle, on the circumference of which the 2n vertices of the polygon are arranged at equal spacing, up to rotation.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

cp's OEIS Frontend

A000939 Number of inequivalent n-gons.

Views

Author

Keywords

Comments

Examples

References

Links

Crossrefs

Programs

Maple

Mathematica

PARI

Formula

Extensions

A094154 Bisection of A000939.

Views

Author

Keywords

Links

Crossrefs

Programs

Maple

Formula

A358328 Triangle read by rows: T(n,k) is the number of polygons with 2*n sides, of which k run through the center of a circle, on the circumference of which the 2*n vertices of the polygon are arranged at equal spacing, up to rotation.

Views

Author

Keywords

Comments

Examples

Links

Crossrefs

A358328 Triangle read by rows: T(n,k) is the number of polygons with 2n sides, of which k run through the center of a circle, on the circumference of which the 2n vertices of the polygon are arranged at equal spacing, up to rotation.