

A200925


Numbers n such that Omega(n) = Omega(n  Omega(n)), where Omega = A001222.


2



1, 3, 6, 30, 35, 40, 45, 51, 57, 60, 66, 78, 87, 88, 93, 95, 102, 104, 105, 117, 121, 123, 136, 140, 143, 145, 156, 161, 174, 175, 185, 187, 203, 205, 215, 217, 219, 221, 232, 237, 245, 249, 258, 261, 267, 282, 285, 289, 291, 301, 303, 305, 321, 323, 325, 329
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OFFSET

1,2


COMMENTS

Omega=A001222: Number of prime divisors counted with multiplicity.
A198327 is a subsequence because, if n and n2 are semiprimes, Omega(n) = 2, and n  2 is semiprime, therefore Omega(n2) = 2.


LINKS

Vincenzo Librandi, Table of n, a(n) for n = 1..10000


EXAMPLE

a(5) = 35 because Omega(35) = 2 and Omega(35  2) = Omega(33) = 2.


MAPLE

with(numtheory):
isA200925 := proc(n)
bigomega(nbigomega(n)) = bigomega(n) ;
end proc:
for n from 1 to 400 do
if isA200925(n) then printf("%d, ", n) ; end if;
end do: # R. J. Mathar, Nov 282 2011


MATHEMATICA

Select[Range[329], PrimeOmega[#] == PrimeOmega[#  PrimeOmega[#]] &] (* T. D. Noe, Nov 29 2011 *)


CROSSREFS

Cf. A001222.
Sequence in context: A065943 A275786 A025555 * A140814 A343433 A136932
Adjacent sequences: A200922 A200923 A200924 * A200926 A200927 A200928


KEYWORD

nonn


AUTHOR

Michel Lagneau, Nov 24 2011


STATUS

approved



