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 A337953 Number of achiral colorings of the 30 edges of a regular dodecahedron or icosahedron using n or fewer colors. 6
 1, 33328, 32524281, 4312863360, 191243490675, 4239501280272, 58236754527707, 563536359633920, 4172726943804861, 25016666666700400, 126431377927701253, 554909560378102656, 2163457078062360639, 7625429483925609552, 24638829565429941975 (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 regular icosahedron and regular dodecahedron are {3,5} and {5,3} respectively. They are mutually dual. There are 60 elements in the automorphism group of the regular dodecahedron/icosahedron that are not in the rotation group. They divide into five conjugacy classes. The first formula is obtained by averaging the edge 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_2^15   Edge rotation*        15     x_1^4x_2^13     Asterisk indicates that the   Vertex rotation*      20     x_6^5           operation is followed by an   Small face rotation*  12     x_10^3          inversion.   Large face rotation*  12     x_10^3 LINKS FORMULA a(n) = n^3 * (15*n^14 + n^12 + 20*n^2 + 24) / 60. a(n) = 1*C(n,1) + 33326*C(n,2) + 32424300*C(n,3) + 4182966200*C(n,4) + 170004083410*C(n,5) + 3156083300916*C(n,6) + 32426546302332*C(n,7) + 205938803790720*C(n,8) + 864860752435680*C(n,9) + 2503126577952000*C(n,10) + 5110943178781440*C(n,11) + 7428048096268800*C(n,12) + 7644417350169600*C(n,13) + 5446616304729600*C(n,14) + 2556525184012800*C(n,15) + 711374856192000*C(n,16) + 88921857024000*C(n,17), where the coefficient of C(n,k) is the number of achiral colorings using exactly k colors. a(n) = 2*A337963(n) - A282670(n) = A282670(n) - 2*A337964(n) = A337963(n) - A337964(n). MATHEMATICA Table[(15n^17+n^15+20n^5+24n^3)/60, {n, 30}] CROSSREFS Cf. A282670 (oriented), A337963 (unoriented), A337964 (chiral). Other elements: A337960 (dodecahedron vertices, icosahedron faces), A337962 (dodecahedron faces, icosahedron vertices). Cf. A037270 (tetrahedron), A331351 (cube/octahedron). Sequence in context: A170798 A043628 A205410 * A210720 A233751 A205212 Adjacent sequences:  A337950 A337951 A337952 * A337954 A337955 A337956 KEYWORD nonn,easy AUTHOR Robert A. Russell, Oct 03 2020 STATUS approved

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Last modified January 18 13:25 EST 2022. Contains 350455 sequences. (Running on oeis4.)