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A064911
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If n is semiprime (or 2-almost prime) then 1 else 0.
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39
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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; internal format)
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OFFSET
| 1,1
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COMMENTS
| a(A100959(n)) = 0 and a(A001358(n)) = 1. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Nov 24 2004
a(n) = A057427(A174956(n)); a(n)*A072000(n) = A174956(n). [From Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Apr 03 2010]
a(n) = A010051(A032742(n)). [Reinhard Zumkeller, Mar 13 2011]
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LINKS
| Reinhard Zumkeller, Table of n, a(n) for n = 1..10000
Eric Weisstein's World of Mathematics, Semiprime
Eric Weisstein's World of Mathematics, Prime zeta function primezeta(s).
Index entries for characteristic functions
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FORMULA
| Dirichlet g.f. (primezeta(2s) + primezeta(s)^2)/2. - Frank Adams-Watters (FrankTAW(AT)Netscape.net), Jun 09 2006
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MAPLE
| with (numtheory):
a:= n-> `if` (bigomega(n)=2, 1, 0):
seq (a(n), n=1..120); # Alois P. Heinz, Mar 16 2011
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PROG
| (Haskell)
a064911 = a010051 . a032742 -- Reinhard Zumkeller, Mar 13 2011
(PARI) a(n)=bigomega(n)==2 \\ Charles R Greathouse IV, Mar 13 2011
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CROSSREFS
| Cf. A064899-A064910, A053409, A046413.
Sequence in context: A102215 A038189 A072783 * A174898 A099618 A106002
Adjacent sequences: A064908 A064909 A064910 * A064912 A064913 A064914
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KEYWORD
| nonn
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com), Oct 13 2001.
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