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A231813 Number of iterations of A046665(n) = (greatest prime divisor of n) - (least prime divisor of n) [with A046665(1) = 0] required to reach zero. 2
0, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2, 2, 1, 1, 2, 1, 2, 2, 2, 1, 2, 1, 2, 1, 2, 1, 2, 1, 1, 2, 3, 2, 2, 1, 2, 3, 2, 1, 2, 1, 2, 2, 3, 1, 2, 1, 2, 3, 2, 1, 2, 3, 2, 2, 2, 1, 2, 1, 2, 2, 1, 2, 2, 1, 3, 3, 2, 1, 2, 1, 3, 2, 2, 2, 2, 1, 2, 1, 4, 1, 2, 3, 2, 3, 2, 1, 2, 3, 3, 3, 3, 3, 2, 1, 2, 2, 2, 1, 3, 1, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

LINKS

Antti Karttunen, Table of n, a(n) for n = 0..16384 (terms 1..1000 from Clark Kimberling)

Antti Karttunen, Data supplement: n, a(n) computed for n = 0..100000

FORMULA

a(0) = 0; for n > 0, a(n) = 1 + a(A046665(n)). - Antti Karttunen, Jan 03 2019

EXAMPLE

A046665(6) = 3 - 2, and A046665(1) = 0, so a(6) = 2.

MATHEMATICA

z = 400; h[n_] := h[n] = FactorInteger[n][[-1, 1]] - FactorInteger[n][[1, 1]]; t[n_] := Drop[FixedPointList[h, n], -2]; Table[t[n], {n, 1, z}]; a = Table[Length[t[n]], {n, 1, z}]

PROG

(PARI)

A046665(n) = if(1==n, 0, my(f = factor(n), lpf = f[1, 1], gpf = f[#f~, 1]); (gpf-lpf));

A231813(n) = if(0==n, 0, 1+A231813(A046665(n))); \\ Antti Karttunen, Jan 03 2019

CROSSREFS

Cf.  A006530, A020639, A046665, A233510.

Sequence in context: A302031 A237353 A293460 * A158210 A322307 A087802

Adjacent sequences:  A231810 A231811 A231812 * A231814 A231815 A231816

KEYWORD

nonn

AUTHOR

Clark Kimberling, Dec 11 2013

EXTENSIONS

Name edited, term a(0)=0 prepended and more terms added by Antti Karttunen, Jan 03 2019

STATUS

approved

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Last modified September 29 10:06 EDT 2020. Contains 337428 sequences. (Running on oeis4.)