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

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A101637 a(n) = 1 iff n is a 4-almost prime, else 0. 15
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Characteristic function of A014613.

See A101638 for the inverse Moebius transform of this sequence.

LINKS

Table of n, a(n) for n=1..100.

Index entries for characteristic functions

Eric Weisstein's World of Mathematics, Almost Prime.

EXAMPLE

a(100) = 1 because 100 = 2 * 2 * 5 * 5 is the product of exactly 4 primes and thus is a 4-almost prime.

PROG

(PARI) a(n)=bigomega(n)==4 \\ Charles R Greathouse IV, Jan 31 2017

CROSSREFS

Cf. A101638, A014613, A000040, A001358, A014612, A014614.

Sequence in context: A085980 A023974 A011730 * A011729 A011728 A133010

Adjacent sequences:  A101634 A101635 A101636 * A101638 A101639 A101640

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Dec 10 2004

STATUS

approved

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

License Agreements, Terms of Use, Privacy Policy .

Last modified March 27 02:08 EDT 2017. Contains 284143 sequences.