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Numbers k such that the fractional part of (3/2)^k decreases monotonically to zero.
22

%I #41 Feb 03 2022 11:57:09

%S 1,2,4,29,95,153,532,613,840,2033,2071,3328,12429,112896,129638,

%T 371162,1095666,3890691,4264691,31685458,61365215,92432200,144941960

%N Numbers k such that the fractional part of (3/2)^k decreases monotonically to zero.

%C Do the values characterize 3/2? If not, what set do they characterize? - _Bill Gosper_, Jul 03 2008

%C Comments from _Eliora Ben-Gurion_, Dec 26 2021: (Start)

%C The numbers have an interpretation in terms of music theory - these numbers characterize integer harmonics that offer monotonically closer approximations to the stacks of just-intonated perfect fifths (3/2). Repeated stacking of this interval forms the basis of the Pythagorean tuning. For example, a(3) = 4; 1.5^4 = 5.0625, therefore the 5th harmonic is close to a stack of 4 perfect fifths. This specific difference is known as the syntonic comma.

%C Likewise, 1.5^29 = 127834.039..., therefore the 127834th harmonic is close to a stack of 29 perfect fifths, but in real life this example is wider than the human hearing range (20 Hz to 20 kHz, 1000 times), therefore lacks practical application. (End)

%t a = 1; Do[b = N[ Mod[(3/2)^n, 1]]; If[b < a, Print[n]; a = b], {n, 1, 10^6}]

%o (PARI) x=1; y=1; a(n)=if(n<0,0,b=y+1; while(frac((3/2)^b)>frac((3/2)^x),b++); x=b; y=b; b)

%K nonn,more

%O 1,2

%A _Benoit Cloitre_, Apr 21 2003

%E More terms from _Robert G. Wilson v_, Apr 22 2003

%E a(16)-a(23) from _Robert Gerbicz_, Nov 21 2010