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 A064911 If n is semiprime (or 2-almost prime) then 1 else 0. 61
 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Antti Karttunen, Table of n, a(n) for n = 1..65545 (first 10000 terms from Reinhard Zumkeller) Eric Weisstein's World of Mathematics, Semiprime Eric Weisstein's World of Mathematics, Prime zeta function primezeta(s). FORMULA a(n) = 1 iff n is in A001358 (semiprimes), a(n) = 0 iff n is in A100959 (non-semiprimes). - Reinhard Zumkeller, Nov 24 2004 Dirichlet g.f.: (primezeta(2s) + primezeta(s)^2)/2. - Franklin T. Adams-Watters, Jun 09 2006 a(n) = A057427(A174956(n)); a(n)*A072000(n) = A174956(n). - Reinhard Zumkeller, Apr 03 2010 a(n) = A010051(A032742(n)) (i.e., largest proper divisor is prime). - Reinhard Zumkeller, Mar 13 2011 a(n) = A280710(n) + A302048(n) = A101040(n) - A010051(n). - Antti Karttunen, Apr 24 2018 MAPLE with(numtheory): a:= n-> `if`(bigomega(n)=2, 1, 0): seq(a(n), n=1..120);  # Alois P. Heinz, Mar 16 2011 MATHEMATICA Table[If[PrimeOmega[n] == 2, 1, 0], {n, 105}] (* Jayanta Basu, May 25 2013 *) PROG (Haskell) a064911 = a010051 . a032742 -- Reinhard Zumkeller, Mar 13 2011 (PARI) a(n)=bigomega(n)==2 \\ Charles R Greathouse IV, Mar 13 2011 CROSSREFS Cf. A010051, A064899-A064910, A053409, A046413, A101040, A105700, A280710, A302048. Sequence in context: A038189 A072783 A288377 * A174898 A099618 A324883 Adjacent sequences:  A064908 A064909 A064910 * A064912 A064913 A064914 KEYWORD nonn AUTHOR Patrick De Geest, Oct 13 2001 EXTENSIONS Edited by M. F. Hasler, Oct 18 2017 STATUS approved

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Last modified July 17 20:45 EDT 2019. Contains 325109 sequences. (Running on oeis4.)