A161925 Numbers n such that largest prime factor of n is also largest prime factor of n-th composite number.

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

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: A326132 A342630 A347807 * 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