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A228487 Trace(pi), where trace is defined in Comments. 4
0, 0, 1, 1, 1, 1, 1, 0, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 1, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

0

COMMENTS

Suppose r > 0.  Let p(n)/q(n) be a sequence of rational numbers with limit r.  Let t(n) be the trace of (p(n),q(n)), and define trace(r) = lim(trace(p(n),q(n))).

The trace of a pair (x,y) of positive integers is defined at A228469 as a 01 sequence determined by the accelerated Euclidean algorithm; specifically, in the steps which take (x,y) to GCD(x,y), a "0" records steps where (u,v)->(v, (v mod u)), and "1" records steps where (u,v)->(v, v - (v mod u)); i.e., "0" if (v mod u) <= v/2 and "1" otherwise.

Conjectures:  (1) trace(pi) is not periodic; (2) if k is a positive integer, then trace(sqrt(k)) is purely periodic; (3) if r is a quadratic irrational, or if r = s*e where s is a positive rational number, or if r = s*e^2 where s is a positive rational number, then trace(r) is eventually periodic.

LINKS

Table of n, a(n) for n=0..85.

EXAMPLE

The first 5 convergents to pi are 3/1, 22/7, 333/106, 355/113, 103993/33102, 104348/33215.  Write these as (3,1), (22,7), (333,106), (355,113), (103993,33102) and apply w to each repeatedly until reaching ( . , 1).  The corresponding 01 words are 0, 00, 00, 001, 001; further convergents yield 0010, 0011, 00111, 001111, and so on, with limit as asserted.

MATHEMATICA

$MaxExtraPrecision = Infinity; r = Pi; z = 800; p = Convergents[r, z]; pairs = Table[{Numerator[p][[k]], Denominator[p][[k]]}, {k, 1, z}]; t[{x_, y_, _}] := t[{x, y}]; t[{x_, y_}] := Prepend[If[# > y - #, {y - #, 1}, {#, 0}], y] &[Mod[x, y]]; userIn2[{x_, y_}] := Most[NestWhileList[t, {x, y}, (#[[2]] > 0) &]]; tt = Map[Map[#[[3]] &, Rest[userIn2[#]]] &, pairs]; t1 = Last[tt] (* Peter J. C. Moses, Aug 20 2013 *)

CROSSREFS

Cf. A228469.

Sequence in context: A287125 A234045 A238468 * A288226 A189078 A257834

Adjacent sequences:  A228484 A228485 A228486 * A228488 A228489 A228490

KEYWORD

nonn

AUTHOR

Clark Kimberling, Aug 23 2013

STATUS

approved

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Last modified June 23 21:29 EDT 2017. Contains 288675 sequences.