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A022447 Fractal sequence of the dispersion of the primes. 2

%I #33 May 20 2019 14:49:50

%S 1,1,1,2,1,3,2,4,5,6,1,7,3,8,9,10,2,11,4,12,13,14,5,15,16,17,18,19,6,

%T 20,1,21,22,23,24,25,7,26,27,28,3,29,8,30,31,32,9,33,34,35,36,37,10,

%U 38,39,40,41,42,2,43,11,44,45,46,47,48,4,49,50,51,12,52,13,53,54,55,56,57,14

%N Fractal sequence of the dispersion of the primes.

%D C. Kimberling, Fractal sequences and interspersions, Ars Combinatoria, vol. 45, p. 157, 1997.

%H G. C. Greubel, <a href="/A022447/b022447.txt">Table of n, a(n) for n = 1..10000</a>

%H Sean A. Irvine, <a href="https://github.com/archmageirvine/joeis/blob/master/src/irvine/oeis/a022/A022447.java">Java program</a> (github)

%H C. Kimberling, <a href="http://faculty.evansville.edu/ck6/integer/intersp.html">Interspersions</a>

%e From _Sean A. Irvine_, May 20 2019: (Start)

%e The prime counting function, pi(n), is iterated (possibly zero times) until a nonprime is reached. If the result of this iteration is m, then a(n) = m - pi(m). Examples:

%e n=11: pi(11)=5, pi(5)=3, pi(3)=2, pi(2)=1. Hence, m=1 and so a(11) = 1-pi(1) = 1.

%e n=12: is already nonprime, hence m=12 and so a(12) = 12-pi(12) = 7.

%e n=13: pi(13)=6 (a nonprime), hence m=6 and so a(13) = 6-pi(6) = 3.

%e (End)

%t m = 30; list = Table[Length[NestWhileList[PrimePi, n, PrimeQ]], {n, m}]; Table[Length@Position[Take[list, k], list[[k]]], {k, Length[list]}] (* _Birkas Gyorgy_, Apr 04 2011 *)

%t primefractal[n_]:= (# - PrimePi[#]) &@NestWhile[PrimePi, n, PrimeQ]; Array[primefractal, 30] (* _Birkas Gyorgy_, Apr 04 2011 *)

%Y Cf. A000720, A022446, A114537, A114538, A114577.

%K nonn

%O 1,4

%A _Clark Kimberling_

%E Terms a(67) onward added by _G. C. Greubel_, Feb 28 2018

%E Offset corrected by _Sean A. Irvine_, May 20 2019

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Last modified March 29 06:57 EDT 2024. Contains 371265 sequences. (Running on oeis4.)