id:A087624 - OEIS Search Results

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a(n)=0 if n is prime, A001221(n) otherwise.

+0
5

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; listen)

	OFFSET	`1,6`
	COMMENT	`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 (reinhard.zumkeller(AT)gmail.com), Oct 17 2008]` `Number of primes that are proper divisors of n. [From Omar E. Pol (info(AT)polprimos.com), 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 (reinhard.zumkeller(AT)gmail.com), Oct 17 2008]`
	MAPLE	`with(numtheory); f:=proc(n) if isprime(n) then nops(factorset(n))-1 else nops(factorset(n)) fi; end;`
	CROSSREFS	`Cf. A001221, A087625.` `A144489 gives partial sums.` `Sequence in context: A114708 A084927 A072670 this_sequence A085122 A083715 A037135` `Adjacent sequences: A087621 A087622 A087623 this_sequence A087625 A087626 A087627`
	KEYWORD	`nonn,easy`
	AUTHOR	`Michele Dondi (bik.mido(AT)tiscalinet.it), Sep 14, 2003`
	EXTENSIONS	`Edited by N. J. A. Sloane (njas(AT)research.att.com), Dec 11 2008`

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Last modified November 25 20:09 EST 2009. Contains 167514 sequences.

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