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A160180 Largest proper divisor of the n-th composite number. 5
2, 3, 4, 3, 5, 6, 7, 5, 8, 9, 10, 7, 11, 12, 5, 13, 9, 14, 15, 16, 11, 17, 7, 18, 19, 13, 20, 21, 22, 15, 23, 24, 7, 25, 17, 26, 27, 11, 28, 19, 29, 30, 31, 21, 32, 13, 33, 34, 23, 35, 36, 37, 25, 38, 11, 39, 40, 27, 41, 42, 17, 43, 29, 44, 45, 13, 46, 31, 47, 19, 48, 49, 33, 50, 51, 52 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Old name: The n-th positive composite number divided by its lowest nontrivial factor.

a(n) = A032742(A002808(n)) = A002808(n) / A056608(n) = A163870(n,A144925(n)). - Reinhard Zumkeller, Mar 29 2014

LINKS

K. Stern, Table of n, a(n) for n = 1..9999

FORMULA

a(n)=n/denom((2^n-2)/n) - Vladimir Kruchinin, Aug 17 2010

EXAMPLE

a(1) = 4/2 = 2, a(2) = 6/2 = 3, a(3) = 8/2 = 4, a(4) = 9/3 = 3, a(5) = 10/2 = 5

MATHEMATICA

f[n_] := Block[{k = n + PrimePi@ n + 1}, While[k != n + PrimePi@ k + 1, k++ ]; k/FactorInteger[k][[1, 1]]]; Array[f, 75] (* Robert G. Wilson v, May 11 2012 *)

PROG

(MATLAB)

function [a] = A160180(k) j = 0; n = 1; while j < k if isprime(n) == 1 skip elseif isprime(n) == 0 j = j + 1; factors = factor(n); lowfactor = factors(1, 1); a(j, 1) = n/lowfactor; end n = n + 1; end - Kyle Stern, May 04 2009

(Haskell)

a160180 = a032742 . a002808  -- Reinhard Zumkeller, Mar 29 2014

CROSSREFS

Sequence in context: A324345 A324533 A141128 * A319351 A323373 A332826

Adjacent sequences:  A160177 A160178 A160179 * A160181 A160182 A160183

KEYWORD

easy,nonn

AUTHOR

Kyle Stern, May 03 2009, May 04 2009

EXTENSIONS

Indices of b-file corrected, more terms added using b-file. - N. J. A. Sloane, Aug 31 2009

New name from Reinhard Zumkeller, Mar 29 2014

STATUS

approved

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Last modified July 9 16:50 EDT 2020. Contains 335545 sequences. (Running on oeis4.)