This site is supported by donations to The OEIS Foundation.

 Annual Appeal: Please make a donation to keep the OEIS running. In 2018 we replaced the server with a faster one, added 20000 new sequences, and reached 7000 citations (often saying "discovered thanks to the OEIS"). Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A087624 a(n)=0 if n is prime, A001221(n) otherwise. 6
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,6 COMMENTS 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). [Reinhard Zumkeller, Oct 17 2008] Number of primes that are proper divisors of n. [Omar E. Pol, Dec 27 2008] LINKS 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] FORMULA a(n) = A001221(n) * A005171(n). - Jason Kimberley, Nov 19 2014 MAPLE with(numtheory); f:=proc(n) if isprime(n) then nops(factorset(n))-1 else nops(factorset(n)) fi; end; MATHEMATICA Array[If[PrimeQ[#], 0, PrimeNu[#]]&, 110] (* Harvey P. Dale, Mar 27 2013 *) PROG (Haskell) a087624 n = if a010051 n == 1 then 0 else a001221 n -- Reinhard Zumkeller, Apr 05 2013 CROSSREFS Cf. A001221, A010051, A087625. A144489 gives partial sums. Sequence in context: A114708 A084927 A072670 * A294891 A294879 A085122 Adjacent sequences:  A087621 A087622 A087623 * A087625 A087626 A087627 KEYWORD nonn,easy AUTHOR Michele Dondi (bik.mido(AT)tiscalinet.it), Sep 14 2003 EXTENSIONS Edited by N. J. A. Sloane, Dec 11 2008 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 December 13 08:08 EST 2018. Contains 318082 sequences. (Running on oeis4.)