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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. 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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