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A131979 A graph substitution group based on a heptagon (Church Music 7 tones; white piano keys) and a pentagon (flats and sharps: black piano keys): the polygons are tied together with 5 connections beside chord connections 12 X 12 matrix substitution with polynomial: 8 + 4 x - 4 x^2 + 9 x^3 - 141 x^4 + 196 x^5 + 35 x^6 - 259x^7 + 265 x^8 - 156 x^9 + 58 x^10 - 12 x^11 + x^12. 1
1, 3, 5, 7, 8, 2, 3, 5, 7, 9, 2, 4, 5, 7, 10, 2, 4, 6, 7, 12, 1, 8, 9, 12, 1, 2, 4, 6, 2, 3, 5, 7, 9, 2, 4, 5, 7, 10, 2, 4, 6, 7, 12, 3, 8, 9, 12, 1, 2, 4, 6, 1, 3, 4, 6, 2, 4, 5, 7, 10, 2, 4, 6, 7, 12, 5, 9, 10, 11, 1, 2, 4, 6, 1, 3, 4, 6, 1, 3, 5, 6, 11, 2, 4, 6, 7, 12, 7, 10, 11, 12, 1, 3, 5, 7, 8, 1, 8, 9 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

As D_6 is two like interconnected hexagons in an hexagonal prism, this figure is an unexpected asymmetry break to that: {6,6}->{7,5}. This sequence has the virtue of tying music theory to both graph theory and a spatial model in group theory. The sequence gives a type of mathematical "model" for 12-tone music theory. It is interesting to note that: binomial(12,8)=495 and dimension of E_8*E_8=496.

LINKS

Table of n, a(n) for n=1..99.

FORMULA

12 Substitutions of the form: 1->{1, 3, 5, 7, 8}; 2->{1, 2, 4, 6}; 3->{2, 3, 5, 7, 9}; 4->{1, 3, 4, 6}; 5->{2, 4, 5, 7, 10}; 6->{1, 3, 5, 6, 11}; 7->{2,4, 6, 7, 12}; 8->{1, 8, 9, 12}; 9->{3, 8, 9, 12}; 10->{5,9, 10, 11}; 11->{6, 10, 11, 12}; 12->{7, 10, 11, 12};

MATHEMATICA

Clear[s] s[1] = {1, 3, 5, 7, 8}; s[2] = {1, 2, 4, 6}; s[3] = {2, 3, 5, 7, 9}; s[4] = {1, 3, 4, 6}; s[5] = {2, 4, 5, 7, 10}; s[6] = {1, 3, 5, 6, 11}; s[7] = {2, 4, 6, 7, 12}; s[8] = {1, 8, 9, 12}; s[9] = {3, 8, 9, 12}; s[10] = {5, 9, 10, 11}; s[11] = {6, 10, 11, 12}; s[12] = {7, 10, 11, 12}; t[a_] := Flatten[s /@ a]; p[0] = {1}; p[1] = t[p[0]]; p[n_] := t[p[n - 1]]; aa = p[4]

CROSSREFS

Cf. A131213.

Sequence in context: A201042 A142340 A185168 * A101496 A218490 A161696

Adjacent sequences:  A131976 A131977 A131978 * A131980 A131981 A131982

KEYWORD

nonn,uned,obsc

AUTHOR

Roger L. Bagula, Oct 07 2007

EXTENSIONS

This is very unclear. Which numbers refer to vertices of the pentagon and which are the vertices of the 7-gon? Once this is straightened out, the entry needs to be edited in the same way that I edited A131213. - N. J. A. Sloane, Jan 25 2012

STATUS

approved

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Last modified October 25 23:29 EDT 2014. Contains 248566 sequences.