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A227417 Integer triples a(3n-2) = n, a(3n-1) = n+4, and a(3n) = n+7. 0
1, 5, 8, 2, 6, 9, 3, 7, 10, 4, 8, 11, 5, 9, 12, 6, 10, 13, 7, 11, 14, 8, 12, 15, 9, 13, 16, 10, 14, 17, 11, 15, 18, 12, 16, 19, 13, 17, 20, 14, 18, 21, 15, 19, 22, 16, 20, 23, 17, 21, 24, 18, 22, 25, 19, 23, 26, 20, 24, 27, 21, 25, 28, 22, 26, 29, 23, 27, 30, 24 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Major chords: If we were to number the musical notes in increasing order of frequency starting with the key of C, we would get C as 1, C# as 2, D as 3 and so on until the next octave. My sequence comprises the keys that would make major chord sounds; for example, a C major chord would be 1,5,8, and a C# major chord would be 2,6,9, and so on.

LINKS

Table of n, a(n) for n=1..70.

Index entries for linear recurrences with constant coefficients, signature (1,0,1,-1).

FORMULA

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

MATHEMATICA

Flatten[Table[{n, n + 4, n + 7}, {n, 33}]] (* T. D. Noe, Sep 03 2013 *)

CROSSREFS

Sequence in context: A119420 A134469 A238166 * A260061 A199379 A198844

Adjacent sequences:  A227414 A227415 A227416 * A227418 A227419 A227420

KEYWORD

nonn,easy

AUTHOR

Yash Deshpande, Jul 11 2013

STATUS

approved

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Last modified September 15 18:22 EDT 2019. Contains 327082 sequences. (Running on oeis4.)