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!)
A337897 Number of achiral colorings of the 8 triangular faces of a regular octahedron or the 8 vertices of a cube using n or fewer colors. 9
1, 21, 201, 1076, 4025, 11901, 29841, 66256, 134001, 251725, 445401, 750036, 1211561, 1888901, 2856225, 4205376, 6048481, 8520741, 11783401, 16026900, 21474201, 28384301, 37055921, 47831376, 61100625, 77305501, 96944121 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

An achiral coloring is identical to its reflection. The Schläfli symbols for the cube and regular octahedron are {4,3} and {3,4} respectively. They are mutually dual.

There are 24 elements in the automorphism group of the regular octahedron/cube that are not in the rotation group. They divide into five conjugacy classes. The first formula is obtained by averaging the cube vertex (octahedron face) cycle indices after replacing x_i^j with n^j according to the Pólya enumeration theorem.

  Conjugacy Class     Count    Odd Cycle Indices

  Inversion              1     x_2^4

  Vertex rotation*       8     x_2^1x_6^1      Asterisk indicates that the

  Edge rotation*         6     x_1^4x_2^2      operation is followed by an

  Small face rotation*   3     x_4^2           inversion.

  Large face rotation*   6     x_2^4

LINKS

Table of n, a(n) for n=1..27.

FORMULA

a(n) = n^2 * (7 + 2*n^2 + 3*n^4) / 12.

a(n) = 1*C(n,1) + 19*C(n,2) + 141*C(n,3) + 394*C(n,4) + 450*C(n,5) + 180*C(n,6), where the coefficient of C(n,k) is the number of achiral colorings using exactly k colors.

a(n) = 2*A128766(n) - A000543(n) = A000543(n) - 2*A337896(n) = A128766(n) - A337896(n).

G.f.: x * (1+x) * (1 + 13*x + 62*x^2 + 13*x^3 + x^4) / (1-x)^7.

MATHEMATICA

Table[n^2(7+2n^2+3n^4)/12, {n, 30}]

CROSSREFS

Cf. A000543 (oriented), A128766 (unoriented), A337896 (chiral).

Other elements: A331351 (edges), A337898 (cube faces, octahedron vertices).

Other polyhedra: A006003 (tetrahedron), A337962  (dodecahedron faces, icosahedron vertices), A337960 (icosahedron faces, dodecahedron vertices).

Row 3 of A337894 (orthoplex faces, orthotope peaks) and A325015 (orthotope vertices, orthoplex facets).

Sequence in context: A159857 A221126 A239418 * A341399 A125384 A126542

Adjacent sequences:  A337894 A337895 A337896 * A337898 A337899 A337900

KEYWORD

nonn

AUTHOR

Robert A. Russell, Sep 28 2020

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 April 22 22:19 EDT 2021. Contains 343197 sequences. (Running on oeis4.)