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.

420, 630, 660, 780, 840, 924, 990, 1020, 1050, 1092, 1140, 1170, 1260, 1320, 1380, 1386, 1428, 1470, 1530, 1540, 1560, 1596, 1638, 1650, 1680, 1710, 1716, 1740, 1820, 1848, 1860, 1890, 1932, 1950, 1980, 2040, 2070, 2100, 2142, 2184, 2220, 2244

Offset: 1

Author

M. F. Hasler, Feb 09 2012

Keywords

• nonn

Comments

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

Links

• M. F. Hasler, Table of n, a(n) for n = 1..18347

Crossrefs

Cf. A200511, A178212.

Programs

Mathematica

Select[Range[2500], PrimeNu[#] == 4 && PrimeOmega[#] > 4 &](* Jean-François Alcover, Jun 30 2013 *)

PARI

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