The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A200521 Numbers n such that omega(n)=4 but bigomega(n)>4, i.e., having exactly 4 distinct prime factors, but at least one of these with multiplicity > 1. 3

%I

%S 420,630,660,780,840,924,990,1020,1050,1092,1140,1170,1260,1320,1380,

%T 1386,1428,1470,1530,1540,1560,1596,1638,1650,1680,1710,1716,1740,

%U 1820,1848,1860,1890,1932,1950,1980,2040,2070,2100,2142,2184,2220,2244

%N Numbers n such that omega(n)=4 but bigomega(n)>4, i.e., having exactly 4 distinct prime factors, but at least one of these with multiplicity > 1.

%C I expect that A123709(a(k))=32.

%H M. F. Hasler, <a href="/A200521/b200521.txt">Table of n, a(n) for n = 1..18347</a>

%t Select[Range[2500], PrimeNu[#] == 4 && PrimeOmega[#] > 4 &](* _Jean-François Alcover_, Jun 30 2013 *)

%o (PARI) is_A200521(n,c=4)={ omega(n)==c & bigomega(n)>c }

%Y Cf. A200511, A178212.

%K nonn

%O 1,1

%A _M. F. Hasler_, Feb 09 2012

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified May 5 14:49 EDT 2021. Contains 343572 sequences. (Running on oeis4.)