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A101637 a(n) = 1 if n is a 4-almost prime, that is a product of exactly four (not necessarily distinct) primes, 0 otherwise. 16
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

Antti Karttunen, Table of n, a(n) for n = 1..65537

Eric Weisstein's World of Mathematics, Almost Prime.

Index entries for characteristic functions

Index entries for sequences computed from exponents in factorization of n

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

EXTENSIONS

Name edited by Antti Karttunen, Oct 08 2017

STATUS

approved

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Last modified November 17 19:40 EST 2017. Contains 294834 sequences.