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A087624
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a(n)=0 if n is prime, A001221(n) otherwise.
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5
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0, 0, 0, 1, 0, 2, 0, 1, 1, 2, 0, 2, 0, 2, 2, 1, 0, 2, 0, 2, 2, 2, 0, 2, 1, 2, 1, 2, 0, 3, 0, 1, 2, 2, 2, 2, 0, 2, 2, 2, 0, 3, 0, 2, 2, 2, 0, 2, 1, 2, 2, 2, 0, 2, 2, 2, 2, 2, 0, 3, 0, 2, 2, 1, 2, 3, 0, 2, 2, 3, 0, 2, 0, 2, 2, 2, 2, 3, 0, 2, 1, 2, 0, 3, 2, 2, 2, 2, 0, 3, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 0, 3, 0, 2, 3
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OFFSET
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1,6
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COMMENTS
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Number of prime divisors of n, but excluding n itself if n is prime.
Number of non-associated primes in the ring Z_n.
Also for n>1 the number of times n is crossed off in the sieve of Eratosthenes (A000040). [From Reinhard Zumkeller, Oct 17 2008]
Number of primes that are proper divisors of n. [From Omar E. Pol, Dec 27 2008]
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LINKS
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N. J. A. Sloane, Table of n, a(n) for n = 1..10000
Index entries for sequences generated by sieves [From Reinhard Zumkeller, Oct 17 2008]
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MAPLE
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with(numtheory); f:=proc(n) if isprime(n) then nops(factorset(n))-1 else nops(factorset(n)) fi; end;
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MATHEMATICA
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Array[If[PrimeQ[#], 0, PrimeNu[#]]&, 110] (* Harvey P. Dale, Mar 27 2013 *)
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PROG
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(Haskell)
a087624 n = if a010051 n == 1 then 0 else a001221 n
-- Reinhard Zumkeller, Apr 05 2013
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CROSSREFS
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Cf. A001221, A087625.
A144489 gives partial sums.
Cf. A010051.
Sequence in context: A114708 A084927 A072670 * A085122 A083715 A037135
Adjacent sequences: A087621 A087622 A087623 * A087625 A087626 A087627
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KEYWORD
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nonn,easy
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AUTHOR
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Michele Dondi (bik.mido(AT)tiscalinet.it), Sep 14, 2003
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EXTENSIONS
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Edited by N. J. A. Sloane, Dec 11 2008
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STATUS
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approved
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