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 A097486 A relationship between Pi and the Mandelbrot set. a(n) = number of iterations of z^2 + c that c-values -0.75 + x*i go through before escaping, where x = 10^(-n). Lim_{n->inf} a(n) * x = Pi. 4
 3, 33, 315, 3143, 31417, 314160, 3141593, 31415927, 314159266, 3141592655, 31415926537, 314159265359, 3141592653591 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS -0.75 + 0*i is the neck of the Mandelbrot set. a(n) is an approximation to Pi*10^n. If you substitute "1/K" in place of "0.1" in the algorithm, the resulting sequence will approximate Pi*K^n. If expressed in base K, the sequence terms will then have digits similar to the digits of Pi in base K. Calculation of this sequence is subject to roundoff errors. In PARI/GP and in C++ using a quad-precision library, the value of A(7) is 31415927, not 31415928 as was originally recorded in this entry. - Robert Munafo, Jan 07 2010 In the PARI/GP program below, if you change "z=0" to "z=c" and "2.0" to "4.0", you get a similar sequence and in addition, A(-1)=0, which is "more aesthetically correct" given the notion that this sequence approximates Pi*10^n. However, such a modified program is NOT equivalent for positive N, it gives A097486(8)=314159267. - Robert Munafo, Jan 25 2010 Terms through a(9) verified in MAGMA by Jason Kimberley, and in Mathematica by Hans Havermann. The difference between the terms of a(n) and A011545(n) = floor(Pi*10^n) is d(n) = 0, 2, 1, 2, 2, 1, 1, 1, 1, 2, 2, 1, 2, ... - Martin Renner, Feb 24 2018 REFERENCES Peitgen, Juergens and Saupe: Chaos and Fractals (Springer-Verlag 1992) pages 859-862. Peitgen, Juergens and Saupe: Fractals for the Classroom (Springer-Verlag 1992) Part two, pages 431-434. LINKS Dave Boll, Pi and the Mandelbrot set Boris Gourevitch, Pi et les fractales, Ensemble de Mandelbrot - Dave Boll - Gerald Edgar Hans Havermann, Computing pi in seahorse valley [From Hans Havermann, Feb 12 2010] Aaron Klebanoff, Pi in the Mandelbrot set (proof) Robert Munafo, Seahorse Valley [From Robert Munafo, Jan 25 2010] MAPLE Digits:=2^8: f:=proc(z, c, k) option remember;   f(z, c, k-1)^2+c; end; a:=proc(n) local epsilon, c, k;   epsilon:=10.^(-n):   c:=-0.75+epsilon*I:   f(0, c, 0):=0:   for k do     if abs(f(0, c, k))>2 then       break;     fi;   od:   return(k); end; seq(a(n), n=0..7); # Martin Renner, Feb 24 2018 MATHEMATICA \$MinPrecision = 128; Do[c = SetPrecision[.1^n * I - .75, 128]; z = 0; a = 0; While[Abs[z] < 2, z = z^2 + c; a++ ]; Print[a], {n, 0, 8}] (* Hans Havermann, Oct 20 2010 *) PROG (MAGMA) A097486:=function(n) c:=10^-n*Sqrt(-1)-3/4; z:=0; a:=0; while Modulus(z)lt 2 do z:=z^2+c; a+:=1; end while; return a; end function; // Jason Kimberley (PARI) A097486(n)=local(a, c, z); c=0.1^n*I-0.75; z=0; a=0; while(abs(z)<2.0, {z=z^2+c; a=a+1}); a \\ Robert Munafo, Jan 25 2010 CROSSREFS Cf. A011545, A299415, A300078. Sequence in context: A207323 A135697 A226508 * A121515 A221883 A002277 Adjacent sequences:  A097483 A097484 A097485 * A097487 A097488 A097489 KEYWORD nonn,more AUTHOR Gerald McGarvey, Sep 19 2004 EXTENSIONS Links corrected by Gerald McGarvey, Dec 16 2009 Corrected and extended by Robert Munafo, Jan 25 2010 Name corrected by Martin Renner, Feb 24 2018 STATUS approved

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Last modified December 1 20:48 EST 2020. Contains 338858 sequences. (Running on oeis4.)