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A054576 Largest proper factor of the largest proper factor of n. 13
1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 4, 1, 3, 1, 5, 1, 1, 1, 6, 1, 1, 3, 7, 1, 5, 1, 8, 1, 1, 1, 9, 1, 1, 1, 10, 1, 7, 1, 11, 5, 1, 1, 12, 1, 5, 1, 13, 1, 9, 1, 14, 1, 1, 1, 15, 1, 1, 7, 16, 1, 11, 1, 17, 1, 7, 1, 18, 1, 1, 5, 19, 1, 13, 1, 20, 9, 1, 1, 21, 1, 1, 1, 22, 1, 15, 1, 23, 1, 1, 1, 24 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,8

COMMENTS

According to the linked MathWorld page, a proper factor can be equal to 1, as is the case for many terms of this sequence, whereas a proper divisor must be larger than 1 (which is not clearly stated on the page defining the latter). - M. F. Hasler, Apr 03 2017

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Eric Weisstein, Proper Factor, on MathWorld--A Wolfram Web Resource.

FORMULA

a(n) = A053598(A053598(n))

a(n) = A032742(A032742(n)); A117357(n) = A020639(a(n)); A117358(n) = A032742(a(n)) = a(n) / A117357(n); a(A037143(n)) = 1, a(A033942(n)) > 1. - Reinhard Zumkeller, Mar 10 2006

PROG

(Haskell) a054576 = a032742 . a032742  -- Reinhard Zumkeller, Jan 31 2015

(PARI) A054576(n)=A032742(A032742(n)) \\ M. F. Hasler, Apr 03 2017

CROSSREFS

Cf. A053598.

Cf. A020639, A032742, A033942, A037143, A117357, A117358.

Sequence in context: A108886 A140886 A001492 * A199515 A316695 A316767

Adjacent sequences:  A054573 A054574 A054575 * A054577 A054578 A054579

KEYWORD

easy,nonn

AUTHOR

Henry Bottomley, Apr 11 2000

STATUS

approved

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Last modified December 13 08:08 EST 2018. Contains 318082 sequences. (Running on oeis4.)