The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A101605 a(n) = 1 if n is a product of exactly 3 (not necessarily distinct) primes, otherwise 0. 22
 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 1, 1, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10000 Eric Weisstein's World of Mathematics, Almost Prime. FORMULA a(n) = 1 if n has exactly three prime factors (not necessarily distinct), else a(n) = 0. a(n) = 1 if n is an element of A014612, else a(n) = 0. a(n) = floor(Omega(n)/3) * floor(3/Omega(n)). - Wesley Ivan Hurt, Jan 10 2013 EXAMPLE a(28) = 1 because 28 = 2 * 2 * 7 is the product of exactly 3 primes, counted with multiplicity. MAPLE A101605 := proc(n)     if numtheory[bigomega](n) = 3 then         1;     else         0;     end if; end proc: # R. J. Mathar, Mar 13 2015 MATHEMATICA Table[Boole[PrimeOmega[n] == 3], {n, 100}] (* Jean-François Alcover, Mar 23 2020 *) PROG (PARI) is(n)=bigomega(n)==3 \\ Charles R Greathouse IV, Apr 25 2016 CROSSREFS Cf. A010051, A064911, (char funct. of) A014612, A101637, A123074. Sequence in context: A115790 A025460 A169673 * A175854 A135133 A011712 Adjacent sequences:  A101602 A101603 A101604 * A101606 A101607 A101608 KEYWORD easy,nonn AUTHOR Jonathan Vos Post, Dec 09 2004 EXTENSIONS Description clarified by Antti Karttunen, Jul 23 2017 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
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified July 31 02:25 EDT 2021. Contains 346367 sequences. (Running on oeis4.)