login
This site is supported by donations to The OEIS Foundation.
Logo

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A080257 Numbers having at least two distinct or a total of three prime factors. 6
6, 8, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, 99, 100 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

COMMENTS

Complement of A000430; A080256(a(n)) > 3.

A084114(a(n)) > 0, see also A084110.

Also numbers greater than the square of their smallest prime-factor: a(n)>A020639(a(n))^2=A088377(a(n));

a(n)>A000430(k) for n<=13, a(n) < A000430(k) for n>13.

Numbers with at least 4 divisors. - Frank Adams-Watters (FrankTAW(AT)Netscape.net), Jul 28 2006

EXAMPLE

8=2*2*2 and 10=2*5 are terms; 4=2*2 is not a term.

CROSSREFS

Cf. A001248, A001221, A001222, A006881, A030078.

Cf. A088381, A088383.

Cf. A000005.

Sequence in context: A071278 A079772 A080731 * A050199 A139118 A089229

Adjacent sequences:  A080254 A080255 A080256 * A080258 A080259 A080260

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Feb 10 2003

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified February 16 10:07 EST 2012. Contains 205904 sequences.