

A199768


Numbers whose greatest prime factor is less than their number of divisors.


0



4, 6, 8, 12, 16, 18, 20, 24, 27, 30, 32, 36, 40, 42, 45, 48, 50, 54, 56, 60, 64, 70, 72, 75, 80, 81, 84, 90, 96, 100, 105, 108, 112, 120, 126, 128, 132, 135, 140, 144, 150, 160, 162, 168, 180, 189, 192, 196, 198, 200, 210, 216, 220, 224, 225, 240, 243, 250, 252
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OFFSET

1,1


COMMENTS

The greatest prime factor equals the number of divisors only for 1 (as defined in A006530) and numbers of the form p^(p1) for p a prime.


LINKS

Table of n, a(n) for n=1..59.


EXAMPLE

4 has 2 as its greatest prime factor, and it has 3 factors (1, 2, 4), so it is in the sequence.
10 has 5 as its greatest prime factor, but it has only 4 factors (1, 2, 5, 10), so it is not in the sequence.


MATHEMATICA

Select[Range[300], FactorInteger[#][[1, 1]]<DivisorSigma[0, #]&] (* Harvey P. Dale, Nov 19 2011 *)


CROSSREFS

Cf. A006530 (greatest prime factor), A000005 (number of divisors), A036878 (p^(p1)).
Sequence in context: A310662 A231569 A100390 * A157932 A097619 A113709
Adjacent sequences: A199765 A199766 A199767 * A199769 A199770 A199771


KEYWORD

nonn,easy


AUTHOR

Franklin T. AdamsWatters, Nov 10 2011


STATUS

approved



