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A071831 Frequency ratios for notes of C-major scale starting at c = 1 (numerators). 7
1, 9, 5, 4, 3, 5, 15, 2, 9, 5, 8, 3, 10, 15, 4, 9, 5, 16, 6, 20, 15, 8, 9, 10, 32, 12, 40, 15, 16, 18, 20, 64, 24, 80, 30, 32, 36, 40, 128, 48, 160, 60, 64, 72, 80, 256, 96, 320, 120, 128, 144, 160, 512, 192, 640, 240, 256, 288, 320, 1024, 384, 1280, 480, 512, 576, 640, 2048 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..66.

OEIS index entry for music.

Index entries for linear recurrences with constant coefficients, signature (0,0,0,0,0,0,2).

FORMULA

a(n+7) = 2*a(n) for n >= 21. - Rick L. Shepherd, Apr 06 2006

G.f.: (15*x^27 +9*x^22 +15*x^20 +5*x^16 +9*x^15 +15*x^13 +3*x^11 +5*x^9 +9*x^8 -15*x^6 -5*x^5 -3*x^4 -4*x^3 -5*x^2 -9*x -1) / (2*x^7 -1). - Colin Barker, Feb 14 2014

EXAMPLE

The ratios are 1 (c), 9/8 (d), 5/4 (e), 4/3 (f), 3/2 (g), 5/3 (a), 15/8 (b); followed by these 7 numbers multiplied by successive powers of 2.

MATHEMATICA

Numerator[2^Floor[#/7]Rationalize[2^((-1+Floor[12(1+Mod[#, 7])/7])/12), 2^-6]]&/@Range[0, 70] (* Federico Provvedi, Feb 14 2014 *)

PROG

(PARI) r=[1, 9/8, 5/4, 4/3, 3/2, 5/3, 15/8]; for(n=0, 10, a=2^n*r; for(m=1, 7, print1(numerator(a[m]), ", "))) - Rick L. Shepherd, Apr 06 2006

(PARI) A071831(n)=numerator([1, 9/8, 5/4, 4/3, 3/2, 5/3, 15/8][n%7+1]*2^(n\7))  \\ M. F. Hasler, Jun 13 2012

CROSSREFS

Cf. A071832, A071833.

Sequence in context: A104139 A244648 A198359 * A245294 A110894 A198933

Adjacent sequences:  A071828 A071829 A071830 * A071832 A071833 A071834

KEYWORD

nonn,frac,easy,nice

AUTHOR

N. J. A. Sloane, Jun 10 2002

EXTENSIONS

More terms from Rick L. Shepherd, Apr 06 2006

STATUS

approved

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Last modified October 20 04:37 EDT 2019. Contains 328247 sequences. (Running on oeis4.)