%I #37 Aug 20 2022 09:00:46

%S 1,2,3,2,3,2,3,2,3,2,3,2,3,2,3

%N Number of black keys in each group of black keys on a standard 88-key piano (left to right).

%C On a standard piano keyboard, the black keys appear in groups of two and three, with each group separated from adjacent groups by the presence of two white keys that have no black key between them.

%C The black keys in a group of two are C#/Db and D#/Eb; the black keys in a group of three are F#/Gb, G#/Ab, and A#/Bb.

%C The A#/Bb key near the left end of the keyboard is a special case; it is the only black key in its group because the white A key to its left is the leftmost key on the keyboard.

%e From _Jon E. Schoenfield_, Aug 12 2022: (Start)

%e In the diagram below, five octaves (i.e., sets of 12 consecutive keys) have been omitted (as represented by the ellipses):

%e .

%e n | 1 2 3 ... 14 15

%e ----+---------------------------------------------------------

%e a(n)| 1 2 3 ... 2 3

%e ______________________________ ... _________________________

%e | |/| | |/||/| | |/||/||/| | | |/||/| | |/||/||/| | |

%e | |/| | |/||/| | |/||/||/| | | |/||/| | |/||/||/| | |

%e | |/| | |/||/| | |/||/||/| | | |/||/| | |/||/||/| | |

%e | |_| | |_||_| | |_||_||_| | | |_||_| | |_||_||_| | |

%e | | | | | | | | | | | | | | | | | | |

%e | | | | | | | | | | | | | | | | | | |

%e |__|__|__|__|__|__|__|__|__| |__|__|__|__|__|__|__|__|

%e A B C D E F G A B ... C D E F G A B C

%e (End)

%Y Cf. A059620, A060107, A060106, A081031, A081032.

%Y Cf. A329207.

%K easy,fini,full,nonn

%O 1,2

%A _Peter Woodward_, Aug 08 2022