A200521 - OEIS

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

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OFFSET

1,1

COMMENTS

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

LINKS

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

MATHEMATICA

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

PROG

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

CROSSREFS

Cf. A200511, A178212.

Sequence in context: A097822 A069064 A024410 * A350374 A189982 A376374

Adjacent sequences: A200518 A200519 A200520 * A200522 A200523 A200524

KEYWORD

nonn

AUTHOR

M. F. Hasler, Feb 09 2012

STATUS

approved