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A115561 a(n) = lpf((n/lpf(n))/lpf(n/lpf(n))), where lpf=A020639, least prime factor. 4
1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 2, 1, 3, 1, 5, 1, 1, 1, 2, 1, 1, 3, 7, 1, 5, 1, 2, 1, 1, 1, 3, 1, 1, 1, 2, 1, 7, 1, 11, 5, 1, 1, 2, 1, 5, 1, 13, 1, 3, 1, 2, 1, 1, 1, 3, 1, 1, 7, 2, 1, 11, 1, 17, 1, 7, 1, 2, 1, 1, 5, 19, 1, 13, 1, 2, 3, 1, 1, 3, 1, 1, 1, 2, 1, 3, 1, 23, 1, 1, 1, 2, 1, 7, 11, 5, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,8

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..10000

Eric Weisstein's World of Mathematics, Least Prime Factor

FORMULA

a(n) = A020639(A054576(n)).

MATHEMATICA

f[n_] := FactorInteger[n][[1, 1]]; Table[f[#/f@ #] &[n/f@ n], {n, 101}] (* Michael De Vlieger, Aug 14 2017 *)

PROG

(Python)

from sympy import divisors, primefactors

def a032752(n): return 1 if n==1 else divisors(n)[-2]

def a020639(n): return 1 if n==1 else primefactors(n)[0]

def a(n): return a020639(a032752(a032752(n)))

print map(a, xrange(1, 102)) # Indranil Ghosh, Aug 12 2017

CROSSREFS

Cf. A014673, A020639, A032742, A054576, A117358.

Sequence in context: A115621 A077565 A316979 * A115622 A294892 A108886

Adjacent sequences:  A115558 A115559 A115560 * A115562 A115563 A115564

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 10 2006

STATUS

approved

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Last modified December 17 14:50 EST 2018. Contains 318201 sequences. (Running on oeis4.)