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A161925 Numbers n such that largest prime factor of n is also largest prime factor of n-th composite number. 1
5, 6, 7, 15, 24, 26, 28, 30, 55, 93, 99, 105, 112, 175, 182, 209, 276, 292, 296, 300, 304, 308, 312, 399, 506, 522, 539, 549, 558, 644, 744, 784, 832, 905, 950, 1156, 1312, 1328, 1369, 1431, 1458, 1485 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

{n: A006530(n) = A006530(A002808(n))} [From R. J. Mathar, May 21 2010]

MATHEMATICA

fi[{a_, b_}]:={FactorInteger[a][[-1, 1]], FactorInteger[b][[-1, 1]]}; Module[ {nn=2000, len, comps}, comps=Select[Range[nn], CompositeQ]; len=Length[ comps]; Position[fi/@Thread[{Range[len], comps}], _?(#[[1]]==#[[2]]&), 1, Heads->False]]//Flatten (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 23 2018 *)

CROSSREFS

Sequence in context: A134985 A111018 A326132 * A078694 A221175 A048007

Adjacent sequences:  A161922 A161923 A161924 * A161926 A161927 A161928

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Jun 22 2009, Jun 27 2009

EXTENSIONS

Corrected (5, 7, 175 inserted) and extended beyond 312 by R. J. Mathar, May 21 2010

STATUS

approved

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Last modified September 29 03:42 EDT 2020. Contains 337420 sequences. (Running on oeis4.)